New power meter - recalculate fitness signature

A few months ago, beginning of may this year, I got a new bike with a new power meter. This new power meter reads significantly lower than the previous one. It is possible that this new one reads a bit low, but I am sure that the previous one read too high.
I am now ready to start preparing the coming season, but my fitness signature is still off.
P.e. a ride that should be something like 100 XSS and 80 difficulty, gives me 70 XSS and 50 difficulty.
Is it possible to recalculate my fitness signature based on my activities since new-bike-day (may 1st 2023), without loosing my history of the previous seasons?

Open this activity in Xert, scroll to the bottom of the page & decrease the Threshold Power value by a little bit (whatever you might estimate the difference to be). Click ‘Save’!

Xert will then re-analyze all the activities since then using the modified TP value & search for BT’s since then.