Are you trying to port forward from the Wifi 6 Boost AP or from the main router itself? Also which Telus router do you have? There are three that are in use with fibre right now and they're not all the same. Are you being told in game that your NAT is moderate? I have a Wifi 6 Boost unit with the T3200 router and I've never had a moderate NAT warning pop up anywhere so far.
Also, PC or Xbox/PS?
The booster is just an access point, to edit any NAT settings you will need to log into the Network Access Hub (NAH) that white box mounted to your wall, to get into it there is a small screw at the bottom of the NAH, if that is removed then it is just 2 clips on either side under the cover, unfortunately the only way to remove the cover is a with a fair amount of force and wiggling. Under that cover is the address and password you will need to edit your NAT settings. The fiber optic line is underneath the NAH so do be careful when removing the cover not to damage the fiber.