Hello,
Following instructions here, should help you set up the VPN.
The graphical interface of Teltonika devices is, of course, different, however most of the steps and configuration options apply.
Keep in mind that you do not need to configure a new interface in step one under Configure the interface section or create a new firewall zone in step 4, as it is done automatically. All of the configurable settings are in Services -> VPN -> Wireguard page.
Best regards,