problem with append func

Hey (:
I placed a text actor on the level. I need to make it so whenever I press on one of the numbers on the keyboard (0-9) that number will appear on the screen in the text actor. for example: if i pressed on “1” the number “1” will appear. and then if I pressed on “2” “12” will appear (2 will be added to the existing 1, not replace him).
i"m having a problem with the append function. I marked the problem using “problem” comment in the picture. the function recives 2 parameters- for the first one, I entered the pressed number and for the second I want to put the existing numbers in the text, but i"m not sure what function can I use to do it. right now the funcntion i used gives me the text actor’s name, so when I press “1” I get “textactor1”.
hope the explanation was clear, eng isn’t my first language.

thanks for the help in advance!