You can access a computer inside a LAN using its IP address. If you don't want to remember addresses like
192.168.20.1 or similar, you can set a hostname for it.
The Host IP address is the IP of the client who should get a name. The Hostname is the clients new name.
The Domain name can be empty. The Hostname will be activated if Enabled is checked.
Click on Add to save the settings.
If you have set up the hostnames correctly, it should look similar to this screenshot.
You will now be able to access a VPN connected host also via its name.