If you don’t like messing with settings on the console, you can use this script to automatically adjust gain:
Automatic gain optimization for dump1090 fa · wiedehopf/adsb-wiki Wiki · GitHub
It adjusts gain until Messages>-3dB are between 1% and 5%.
This usually equates to a good gain setting, it basically follows the guidelines of the 2nd post of this thread (Thoughts on optimizing gain).
Anyway for the manual method, i’ve written small helpers as well, they are included here:
Automatic installation for dump1090 fa · wiedehopf/adsb-wiki Wiki · GitHub
(@abcd567 feel free to include the helper for setting gain on the console without editing a file, if you wish you can include the location changer as well though this isn’t normally needed with piaware installed)