Yes, you want to manually select a BT workout and ride it in Slope mode, exceeding targets where able (without blowing up), then spin up and go all out (for at least 5-7 seconds) on the interval(s) designed to drive you to failure point, right before you are about to collapse (
to 
).
XATA will warn you (below your name on xertonline.com) if you haven’t generated a BT in over three weeks. Some users generate BTs while training due to ZRL events, group ride sprints, or maximum crest-of-hill efforts. For the rest of us 
you want to select a BT workout on occasion to force the issue. Search the Workout Library for “fitness test” (in quotes) to locate the default BT test workouts.
Lots of newbie tips in this thread –
Beginner questions - Support - Xert Community Forum (xertonline.com)
Reference –
Breaking Through the Xert Way! – Xert (baronbiosys.com)