To unblock a user, please follow these steps:
Click on ‘Settings’ in the menu list on the left side right underneath your profile picture/icon.
Scroll down and click on the 'Edit' button next to 'Manage blocked users'.
You will now be able to manage your users that you have blocked.
You should see a pop-up that confirms that the user is now unblocked
Or you can go to the profile of respective user, click on the three dots next to their username, and choose ‘Unblock user’.