How to change value in mysql based on another value in the same database?

I am trying to change one of the value in my table in database based on an another value in the same database but different table. The first table is called orders and the second is called buy supply. What I want to do is I want to change the value of sumquantity that is in 'buysupply' table by subtracting a value from the column named quantity_ordered from 'orders' table. I tried writing some query but it is not working, it keeps popping up error. If you know of a solution, do let me know. The code is all below as well

private void DispatchButtonActionPerformed(java.awt.event.ActionEvent evt) {                                               
String type = txttype.getSelectedItem().toString();
String name = txtname.getText();
String quantity = txtquantity.getText();
String dispatch_row = txtdispatch.getText();
String statusDispatched = "Dispatched";
try {
Class.forName("com.mysql.jdbc.Driver");
con1 = DriverManager.getConnection("jdbc:mysql://localhost/restock", "root", "password");
// Focus on this 
String template = "UPDATE orders SET status = '%s' WHERE id = %s";
String template2 = "UPDATE buysupply SET sumquantity = sumquantity - %s WHERE id = %s";
String quantity_ordered = "quantity_ordered FROM orders";
pst = con1.prepareStatement(String.format(template, statusDispatched, dispatch_row));   
pst.executeUpdate();
pst1 = con1.prepareStatement(String.format(template2, quantity_ordered , dispatch_row));
pst1.executeUpdate();
// Look on top
JOptionPane.showMessageDialog(null, "Item has been dispatched");
// To update the newly recorded data to the table
table_update();
// Set the textfields to empty upon button click
txttype.setSelectedIndex(-1);
txtname.setText("");
txtquantity.setText("");
txtdispatch.setText("");
txttype.requestFocus();
} catch (ClassNotFoundException | SQLException ex) {
JOptionPane.showMessageDialog(null, "Quantity or Dispatch field is not an integer, Please try again.");
Logger.getLogger(mainpage.class.getName()).log(Level.SEVERE, null, ex);
}
}  
// This code is in another class file
try {
Class.forName("com.mysql.jdbc.Driver");
con1 = DriverManager.getConnection("jdbc:mysql://localhost/restock", "root", "password");
String template = "SELECT SUM(quantity) as sumquantity FROM buysupply WHERE itemtype IN ('Plastic gloves', 'Rubber gloves')";
PreparedStatement pst = con1.prepareStatement(template);
ResultSet rs = pst.executeQuery();
if (rs.next()) {
glovesum = rs.getString("sumquantity");
} else {
System.out.print("Query didn't return any results");
}
} catch (ClassNotFoundException | SQLException ex) {
Logger.getLogger(stock.class.getName()).log(Level.SEVERE, null, ex);
}

As far I understand (and please read until the end) if it is a classic Invoice order database with a list of product into "buysupply" table and "order" table for the ordering client list of product.
The first point, several people into the comment point is the missing link data between both table. I assume reading your peace of code that the link is made by a ID but that not clear, so I offer a solution base on a link between those columns:

orders.itemtype = buysupply.itemtype

If it on an other element, please change the information into the SQL query below.
I assume also the column orders.status as to change the values from what I call 'Waiting' value to 'Dispatched' value.

So here the data before into "buysupply" table:

id, itemtype, quantity
1 , mask , 704
2 , clothed, 101
3 , N95, 18

Here the data before into "order" table:

id, itemtype, quantity_orderred,  status, 
1,mask, 1 , Dispatched
2,clothed,3,Waiting

The SQL to update both value (the orders.status and buysupply.quantity ) should be something like that suppose the order.id to update is 2:

update orders,buysupply 
set orders.status='Dispatched', 
buysupply.quantity = buysupply.quantity - orders.quantity_orderred
where  
orders.itemtype = buysupply.itemtype
AND
orders.status = 'Waiting'
AND
orders.id = '2'

AFTER:
So here the data after into "buysupply" table:

id, itemtype, quantity
1 , mask , 704
2 , clothed, 98
3 , N95, 18

Here the data before into "order" table:

id, itemtype, quantity_orderred,  status, 
1,mask, 1 , Dispatched
2,clothed,3,Dispatched

The update could apply on several tables and columns, you should just indicate the column table name with each column to avoid confusion.

That could be the first step to let you improve the code for the sum part, that, I afraid no understand at all.

Then I find a partial information explaining that the sum_quantity is a computed calcul from a sum of the value, so you do not want to change the quantity, my bad.

So you can create a temporary table with this kind of SQL, temporary table is detroy at the connection close:

CREATE TEMPORARY TABLE IF NOT EXISTS TMPsumquantity AS 
SELECT SUM(quantity) as sumquantity FROM buysupply WHERE itemtype IN ('Plastic gloves', 'Rubber gloves') 

That could create a column with the information you want, BUT, it's not my recommendation as far I understand

I will create a new column to store the sum value into the table "buysupply", to say the "the quantity in stock avalaible at the moment this order will be Dispatched is that for this element" so the result of you sum value

Before "buysupply":
id, itemtype, quantity, quantity_avalaible
1 , mask , 704, 704
2 , clothed, 101, 101
3 , N95, 18, 18

Before "order":
id, itemtype, quantity_orderred, status, quantity_avalaible
1,mask, 1 , Dispatched
2,clothed,3, Waiting

So the SQL to create this column is complex, base on an inner-join between the same table

UPDATE buysupply b1
INNER JOIN (
SELECT SUM(quantity) as sumquantity, id
FROM buysupply
where  buysupply.itemtype  IN ('clothed', 'N95')       
) b2 ON true
SET b1.quantity_avalaible = b2.sumquantity

So the new table "buysupply" with the colum "quantity_avalaible" containing the sum of the value of the colum quantity for N95 and clothed values :

id, itemtype, quantity, quantity_avalaible 
1 , mask , 704, 116
2 , clothed, 101, 116
3 , N95, 18, 116

So then you can use the first SQL proposal to update quantity_avalaible depending the value of "orders.quantity_orderred"

Last point, I have a partial view on the data structure and the bussiness logic, it could be usefull to store a negative value into the column "orders.quantity_orderred" so the SQL SUM could add and substract values with the same call to the SUM function

Best