Do you have a public IP ? What are the first two digits if you go to a site like https://v4.ident.me/ ?
If you have a static public IP, you forward a port in our router to the fixed local IP of your OS, say port 121 for instance, then you can connect to it from outside the lan or from the android app using your_ip:121
If you have a dynamic public IP, you need to setup an account with noip, dyndns etc with your own alias, say myLANip.dynddns.org, and setup your router to refresh it when it changes, then you can connect to it using myLANip.dynddns.org:121.
If you don’t have a public IP, such as your double natted behind an LTE connection, you are out of luck I am afraid, you can only setup a small pc or raspberry always on in your lan with anydesk, teamviewer, remote.it etc, and use it to log into your OS.
See my other post on this very topic.