How to resolve the following program with a for loop into producing an appropriate output?

The following Java program is supposed to manipulate a string input by the user in such a way that the user will decide which character needs to be replaced with another and just the last character from the string should be replaced. Example if the user enters the string "OYOVESTER" and decides to replace "O" with "L", the program should output the following result: "OYLVESTER" (notice that only the last "O" was replaced with "L")

NOTE: YOU CANNOT USE BREAK COMMAND TO STOP THE LOOP. IT IS PROHIBITED.

import java.util.Scanner;
public class StringFun {

	public static void main(String[] args) {
		Scanner keyboard = new Scanner(System.in);
		
		System.out.println("Enter the string to be manipulated");
		String inString = keyboard.nextLine();
		String outString = "";
		
		//Replace Last
		System.out.println("Enter the character to replace");
		char oldCharF = keyboard.next().charAt(0);
		
		System.out.println("Enter the new character");
		char newCharF = keyboard.next().charAt(0);
		
		int count = 0; // variable that tracks number of letter occurrences
		for(int index = inString.length() - 1;index >= 0;index--) {
			if(inString.charAt(index) == oldCharF && count < 1){
				outString = newCharF + outString;
				outString = outString + inString.substring(0,index);
				count++;
				
			}
			if (count < 1) {
				outString = outString + inString.charAt(index);
			}
			
		}

		System.out.print("The new sentence is: "+outString);
		

	}

}

I keep getting the following output which is incorrect:

Enter the string to be manipulated

OYOVESTER

Enter the character to replace

O

Enter the new character

L

The new sentence is: LRETSEVOY

There are many simpler ways to achieve your requirement but I hope you have to demonstrate this with loops (without breaks)

Then you can use some thing like this :

boolean skip = false;

for (int index = inString.length() - 1; index >= 0; index--) {
  if (!skip && inString.charAt(index) == oldCharF) {
    outString = newCharF + outString;
    skip = true;
  }
  else {
    outString = inString.charAt(index) + outString;
  }
}

PS : Using String concatenation inside loops is not recommended since
every String concatenation copies the whole String, usually it is preferable to
replace it with explicit calls to StringBuilder.append() or StringBuffer.append()

No break command seems like a weird condition. You could just a boolean value, and other methods, to break the loop when you need. Why not do something like this?

public static void main(String[] args) {
    Scanner keyboard = new Scanner(System.in);

    System.out.println("Enter the string to be manipulated");
    String word = keyboard.nextLine();

    //Replace Last
    System.out.println("Enter the character to replace");
    char oldCharF = keyboard.next().charAt(0);

    System.out.println("Enter the new character");
    char newCharF = keyboard.next().charAt(0);

    int index = word.lastIndexOf(oldCharF);
    if(index > 1){
        word = word.substring(0,index) + newCharF + word.substring(index+1);
    }

    System.out.println("The new sentence is: " + word);
}