taken directly from the offical 390 m33 package found on QJ:
"- Get the 3.80 sony update from somewhere, and put it in same folder, with name "390.PBP"."
if i read that right, it says, find a fresh 3.80 update file and rename it for 3.90.
is this some typo? because i did that and when i loaded it, it said verifying 3.90PBP, Incorrect File.