I had a similar problem as described by several users above, because I decided to name my P3A after I already had done 2 flights. This resulted in 2 lists in my flight log. The one without a name and the rest with the current name of my drone. Here a description how it worked for me to merge the flight records from different drone names - no guarantee!!:
As a prerequisite, you need all flight records as a txt file. Save them on your desktop computer. Then erase the flights in the "wrong" (old) list in the DJI go app of your mobile device (im my case the 2 first flights where the drone was nameless). Close the app an open it again. The whole second list (and in my case the 2 first flights) should be gone. Copy the (in my case 2) txt files from your flights which were done under another drone name back to the tablet/phone and restart the app. Bingo - the two "nameless" flights are now in my current flight list.
Hope this worsk for you as well!
Tschens