Assistant 2 does not work with P3's. You need to copy the .bin file to an SD card. See the link below for the firmware .zip files.i tried assistant2 it asked for a license number, what license number?
Im sure it was not this hard last time a few years ago...
Extract the .bin from the .zip. Put the bin file on the SD card. Put the SD card in the aircraft and power up. The upgrade should start immediately. ( Caution ) When you do the upgrade it would be advisable to use a small fan to keep the gimbal cool. It might take a while for the update to finish.
Scroll to the bottom of the page for the firmware: P3 Firmware