You cannot block or unblock contacts via the Zoom web portal (zoom.us). You use the Desktop Client or the Mobile App to manage your contact list.
By default, if a host removes a participant from a live meeting, that person cannot rejoin. To change this for future meetings: Blocking and unblocking spam numbers in Zoom: how to unblock someone on zoom
Select and tap the Unblock button next to the relevant contact. 2. How to Unblock a Phone Number You cannot block or unblock contacts via the