Adding names to the high score

Hello guys! I have a really simple question, but I can't find it anywhere, or rather just don't know what to search for.

Anyway, I'm trying to create a really simple high score, just the initials of the player, but I can't count on the keyboard to do it because I want the game to be fully playable using only the controller. My problem is finding a way to create a name by choosing letter by letter and then sending this to the high score. Any ideas?

Thanks in advance!