Yes, you can manually remove a contact from your blacklist. To do so, follow our tutorial: How to unblacklist subscribers.
Note: Consider well why you want to remove a contact from the blacklist. If they are blacklisted it is for a reason. If their address is not valid your next email will result as a hard bounce and this will affect your reputation and your number of credits. If you reinsert a contact who had asked to be removed from your database, you are taking an action against their will and this is illegal.