you can't apply for an unban. These topic's description says: "Post here if you require technical assistance.". If you think that ban was not appropiate, please post a thread in "Report a Staff member". But please provide more details such as the ban length, reason and date if you can.
If it is not, you can't get your friend unbanned.
Btw, i didn't answer you in-game as you've asked me more than 10 times in-game. Please use the forum for such questions as every user can read + answer here.