@Edward Bonel - A board's link, i.e., unique ID, cannot be changed. You can, however, duplicate the board which will result in a new ID/link

And, since you are concerned about people who have left your company still having access to a board, I will assume that you removed them from your Miro team space, but the boards would be accessible because you have visitor access enabled. Rather than deleting the original board, I would suggest that you disable visitor access, and even restrict it to those who need access to the original for recovery purposes.