How do I approve a follower request?
If your account is set to private, anyone who wants to see your photos or videos will have to send you a follower request that will appear in your News Feed.
To approve/deny the request, just tap on the username of the user who requested to follow you. You'll be brought to their profile page, at the top of which you should see the Approve and Deny options.
If you accidentally deny a follow request, ask the person to request to follow you again.