My friend have his own Facebook Page, he mistakenly post something which go against of community standers, now he got a block for 30 days. How to unblock him?
As you said, your friend have violated Facebook Community Standards, and that's why he has been blocked. There is no way to get unblocked other than waiting. Don't do anything otherwise you might get blocked permanently.
The block is temporary, but it can't be lifted for any reason, so you'll need to wait until the block is finished.