change your router control panel vpn settings remotely with server selection menu

Hi,

I wanted to ask a question about a vpn. Somehow black vpn provider has a way to remotely connect to the router and change servers from a drop down menu in dd-wrt firmware. I was curious if anyone knows how or what software can do that. I have a Asus Rt-AC68W wireless router . Dd-wrt don't have the extras like dual wan and 4g broadband modem support. I picked up a usb modem in case of emergencies situations because my phone doesn't pick up 4g and I have to use the router for my phone in case of medical emergency.

But if anyone can help me with that software information I would be grateful for the help.

Thank you

Have a great day!