Try this :
0BC9: samp send_dialog_response dialog 0@ button 1@ listitem 2@ input ""
Usage :
0@ [int] - dialog id //0 for current I guess
1@ [byte] - button (0 - right, 1 - left\central)
2@ [int] - number of element from list
"" [string] - optional par, goes for text you did type in dialog