Change a characters in a text

[Jhon Carlo]

I need to change a character at a time, with buttons, in a text, for example:

abcdefg

With button 1) change only the letter "a" but not the other letters;

With button 2) change only the letter "b" but not the other letters;

etc.

I have seen several methods that are not in my case.

I would like some advice to know, except obviously  the script of buttons, what is the easiest method to solve this problem.

Thanks.

[Ned Murphy · Accepted solution]

You can look into using the String.replace() method.  Another option is to just use String.split(remove_letter).join(replacement);

[Jhon Carlo]

Thank you Ned, you helped me find the solution! 

[Ned Murphy]

You're welcome Jhon