how do I change ownership of contacts from users who are no longer in the CRM

how do I change ownership of contacts from users who are no longer in the CRM

I had user A
user A owned contacts X Y Z *
user A is gone
I want to find and change all contacts XYZ * to user B

I can't search for contact owner A as CRM does not allow me to do that

How do I change all contacts(X, Y and Z) owned by A to user B?