Can't connect Ring Doorbell 2 to new Comcast Modem XB7

I had to get a new comcast modem last week. The model is XB7. It has the 2.4 and 5 ghz combined. I can't get my Ring Doorbells to recognize the new modem. Comcast techs could not help me. Like they never heard about it. I was able to get into the xfinity gateway app to add a device. However the 1st field is "Add Domain Name". I have no idea what the Domain Name and neither did Comcast. Anyone come across this issue? Thanks Jim