I’d suggest loading some historical data and see what Xert analysis comes up with for a starting signature. If the numbers are off there are several ways to manually adjust a signature and move forward from there.
Traditional FTP tests are not required in Xert but you can select a “fitness test” workout to confirm your signature is in the right ballpark.
Ride the workout in Slope mode exceeding target watts and duration (if able) on any intervals designed to drive you to a failure point. For sprint efforts try to hold max watts for at least 5-7 secs.
Lots of newbie tips in my onboarding post here –
Onboarding steps for Xert trial users and newbies - General - Xert Community Forum
Welcome aboard. 