Hi.
They don’t appear to have info about the config files on their site.
If you are a subscriber to their VPN, send them an email and ask them for either OpenVPN configuration files or Wireguard configuration files for Android.
Once you have one of those two you can follow the guide on gl.inet support page on how to install them (depending if you get openvpn or wireguard).
This depends on your VPN provider’s ability to supply those files to you in the first place.
If you have an account with them maybe they have a Client Area on their main web page where you can login and search there for the config files.
Just email them first and see what they say.