I want to send "I have it" when "xlsx A1~A500" matches the user ID

import discord,openpyxl
client = discord.Client()
@client.event
async def on_message(message):
    if message.content.startswith("$text"):     
        wb = openpyxl.load_workbook('test.xlsx')
        sheet = wb['Sheet1']
        for i in range(2, 501):
            heng = sheet[f"A{i}"].value
            if heng == f"#{message.author.id}": 
                await message.channel.send(f"{i}: I already have it.")
                break # <--problem 
            else:
                wb = openpyxl.load_workbook('test.xlsx')
                sheet = wb['Sheet1']        
                next_row = sheet.max_row + 1
                sheet[f"A{next_row}"].value = f"#{message.author.id}"
                next_row += 1
                wb.save('test.xlsx')
                await message.channel.send("Information has been generated")
                break

Maybe because of the "break" under "if", the repeat statement is interrupted, so only the xlsx file "A2" is recognized.

I want to send "I have it" when "A1~A500" matches the user ID.

I think there's a few fundamental issues with your script.

On the first iteration of the for loop, i is 2. We check that A2 is equal to the author's user ID and if it is we post a message saying it is and exit. If it isn't, then we automatically add that ID to the end of the sheet. I tested this locally with my own test.xlsx that only add a column name in A1 and max_row was always 2 (the next empty cell) and so by adding one to that - you're inserting the name at A3. So the next time you send a message, we check A2, and as it's not there we decide to insert the name again - but this time at A4. And so on and so forth.

So I've made some improvements on the loop:

import discord
import openpyxl

client = discord.Client()
@client.event
async def on_message(message):
    if message.content.startswith("$text"): 
        author_id = message.author.id
        wb = openpyxl.load_workbook('test.xlsx')
        sheet = wb['Sheet1']
        for i in range(2, 501):
            heng = sheet[f"A{i}"].value
            if not heng:
                # the cell is empty!
                # is this the end of the data?
                # insert user here
                sheet[f"A{i}"] = f"#{author_id}"
                wb.save('test.xlsx')
                await message.channel.send(f"Inserted {author_id} user at A{i}")
                break
            elif heng == f"#{author_id}": 
                # found a cell that contains our data
                await message.channel.send(f"{i}: I already have it.")
                break
            else:       
                # else statement is largely irrelevant here - but keeping for demonstration
                # heng is equal to a different username
                continue

This works a bit better:

• starting at 2, we're looking at all the rows in column A
• if the cell is empty - this assumes this is the end of the data and there's nothing after it; so we insert our author ID here
• if the cell isn't empty - check it's equal to our author ID. If it is; then we found it - hurray!
• otherwise, check the next row down

I've tested this locally and this seems to do what you want it do now.

There are still some improvements to be made:

• if you had over ~500 unique users, then it's possible it would never find the user ID as it would reach the end of the range if all the other cells have other users in them
• assumes an empty cell means end of the list - but might not necessarily be the case