Recommend you make sure you have your logbook backed up before doing this.
1. Go into preferences under the "Time" tab and select "PICUS" column for display, also select "autofill from total time". (It's called "PICUS" in my version because it knows I'm Australian, yours may be P1/US or something.)
2. Create a smart group that gives you the flights you are interested in, e.g., display flights with you as the handling pilot and in the appropriate aircraft type and/or appropriate date range.
3. In the smart group folder, select all of the flights by selecting the top one then using SHIFT+select for the bottom one. Unlock them if required.
4. In the PICUS field you should be able to insert the curser and type a space. This should fill the PICUS field with the total time from each selected flight.
5. Delete the P2 field for all selected flights by inserting the curser and typing 0.
6. If you balls it up, restore from your backup
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I tested this on my own version of Logten and it worked but I didn't use a smart group, just did it on the main logbook page. Tread carefully.