Using xFi gateway with Orbi RBR750 mesh system

We recently upgraded to Xfinity xFi   Gateway After we were told that our system would work much better and could handle traffic more efficiently. After multiple unsuccessful chat conversations with Xfinity tech team, I am reaching out to better understand as to how properly set up my Orbi RBR750 and xFi complete To work together. Though my Xfinity app shows fast speed, All the other means of checking the speed shows considerable slow down.  Any particular settings set up in the Orbi RBR750 mesh, or the XFi complete modem is appreciated. I have also noticed most of the devices connecting to the Orbi as a preferred Wi-Fi connection.  Anyone with expertise,  if you could be so kind and provide step-by-step setting changes that I need to make or any other alterations that you feel may need to be made in order for my system to work properly