Got to do the P4 first like every other Phantom. Downgrade the firmware in the RC.
Hopefully you have an android tablet to update from. I had both an android tablet and a IOS tablet. The IOS Ipad with the old Go app seems to be the issue. I switched to my android tablet and reloaded the GO app from the DJI Web page (new go app) everything loaded with no issues.I'm having the same problem others have mentioned. Lost connection and update fail in the assistant app.