I set it directly in /opt/retropie/configs/all/retroarch-joypads/THTTHTArcadeconsole2PUSBPlayer.cfg
input_enable_hotkey_btn = "8"
If I use the Retroarch menu (Settings/Input/Input Hotkey Binds/Enable Hotkeys), I can't set it to 11 because is on js1. I can only set button from js0.