In your ~/.config/gzdoom/gzdoom.ini file, if you do not have these four sections  create them at the end. If they are there, you can just update the keybindings. It should look like this:


[Doom.PBInteractions.Bindings]

[Doom.PBInteractions.DoubleBindings]

[Doom.PBAdvMoves.Bindings]
F=+User2
G=+User1
U=unreloader
V=+User4

[Doom.PBAdvMoves.DoubleBindings]