To update the text inside an EditText, you must use the setText() method. If you pass in a string, then it will update the text to that string. If you pass in a reference to another EditText, then it will replace the text inside that EditText with whatever is inside of your other EditText.
If you want to change only one character in an EditText, then you can use setText(char) and pass in a single character as the argument. For example:
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