Change keybind with any letter on keyboard?

I am making a game and I want my users to be able to change a keybind on a textbox, but I don't know how I would make it so if they clicked say: Ctrl. Then it would change the text to the button. Usually it wouldn't do anything.

I am thinking its something upon recording the input on the text. I just don't know link would be nice.

Still need help!