You can flag the activities on file with the bad data so they are not incorporated into your signature calculations.
Easiest way to do that is select Activities, Table in sidebar menu, sort by Peak Power then flag those entries with power spikes.
The other way to reset would be to locate your last breakthrough, select Advanced MPA tab, and seed that activity with the signature numbers you want to use moving forward.
See this thread –
When to use the "extract"button in "advancede mpa"tab - General - Xert Community Forum (xertonline.com)