Go to Settings & Privacy → Visibility → Blocking, enter your password, and tap Unblock next to the person’s name.
Note: You’ll need to wait 48 hours to block them again, and you must send a new connection request if you want to reconnect.
To unblock someone on LinkedIn, go to Settings & Privacy, select Visibility, then Blocking. Enter your LinkedIn password, find the blocked profile, and click Unblock. Note that you can only unblock the same person after 48 hours.