When you unblock someone, that person will be able to see your posts on Facebook that you share with the public. The person won’t automatically become your friend on Facebook. If you want to become friends with a person who you’ve unblocked, you’ll need to send them a friend request.
How To Unblock Someone On Facebook Android App
To unblock someone using Android App:
Tap on this icon
Scroll to the bottom and tap Account Settings > Blocking
To unblock someone, tap Unblock next to their name.