Trying to use my own router

Hello I currently live in a Wi-Fi ready apartment with fiber, and I’m trying to use my own third-party router which is a tp link I currently have it set up in bridge mode with the XB7 But I am trying to bypass it and plug in directly to the ONU unit. I have contacted Comcast and they told me it’s impossible to do this, but I know it’s not true because I’ve seen people on this forum able to do it, so please help