How do i manually add the MAC address of my printer to the list of permitted devices for my new wireless router???

I have an HP printer that is unable to connect to my wireless router.  How do I enter this or have someone from xfinity enter this so I can use my printer again?  This seems like a really unreasonable amount of hoops to jump through to get my printer recognized!!   Very frustrated that there is no direct phone number to contact someone for help, need this problem fixed immediately!!!