HP Printer blocked

I have HP 8620 printer.  It worked wirelessly with xfinity router from last year.  Then we got a new xfinity router (put in by xfinity). And my printer will not connect.  Printer spit out a page explaining problem and says that maybe router has blocked the MAC address and says to go in and enable the printer's address.  HOW DO I DO THAT?  I don't remember ever being told by the Xfinity technician that I had an admin log in ID or password.  This must be a common problem!!!  It is enough to leave and go to ATT.  Have spent hours trying to figure it out.