How to instantiate prefab over the text one letter at a time? OR how to get transform of letters in a text

I am making a typing game. I have figured out how to check if the player is typing the correct letters/alphabets or not. Right now I am logging into the console "Correct" or "Incorrect." I would like to instantiate a green box prefab over the letter/alphabet if it's typed correctly and a red box prefab if it's typed incorrectly.

THIS IS WHATS HAPPENING IN THE CODE - 1. Takes a string and converts it into an array of char 2. Take user Input and compare it to the array char values.

Btw - i am using C#