This guide explains how to remove a contact from your blocked list on WhatsApp so you can receive messages and calls from them again.
Alternatively, if the chat is open, you may see a system message at the bottom stating "You blocked this contact. Tap to unblock." Tapping this will prompt a confirmation to unblock. how to unblock contacts on whatsapp
Open and go to the chat of the person you want to unblock. This guide explains how to remove a contact
This is the fastest way if you still have an active chat thread with the person. if the chat is open