Xert’s signature algorithm analyzes maximal efforts all along your power curve to establish PP, HIE, and TP values.
If your imported history lacked a wide range of max effort data points you can ride the standard Ftiness Test workout indoors in Slope mode to validate your signature. Or generate a simiilar effort outdoors. I.e. two max sprints (7-10 secs) with full rest-in-between (RIB), then four escalating intervals >TP with short RIBs until you reach a complete failure point on the final interval.
For details see: From old trainer to smart trainer. Set FTP - #5 by ridgerider2
Four Breakthrough Types: Breaking Through the Xert Way! – Xert:
Once your signature is dialed in your normal riding activities should suffice for signature adjustments as long as they include occasional maximal efforts at various points on your curve.
There are lots of blog articles that discuss the science behind Xert.
E.g. The Science: The Physiology Behind Focus and Strain, and How To Train The Metabolic Pathways – Xert