well inside the house you make a nice event.
you change the graphics into a human and choose action key or hero touch
and then you do...
A FREAKING MESSAGE BUTTON
if it wasn't horrible enough that 1 person was enough of an idiot to ask how to use the message button now it's a new fashion..
also if you meant letter, and i hope for you that you did then the graphic event should look like:
if swtich(letter) = on then
-message: omfg i already gave you the letter shoot me!!!
else
-change items: +letter
-message: yay you got the letter now go away before ill eat your brain