In case you would like to have PPTP VPN server but no such is installed. But first things first. For such an obsolete hardware and software keep in mind that accessing it requires passing old host key algorithms and cipers. Then: If you have other VPN types enabled, better disable it as you will be using PPTP and not SSTP or OpenVPN/WireGuard. Now, for HTTP access, most of the time it will be configured for local network access only. We can change this: Changing HTTP UI port to something different than default will give us ability to run other service
If you own this router then you might be interested how to setup VPN Server. I am personally interested in a way of how to do this using CLI only. It looks easy however there is one odd settings you should be aware of. To start with, it will be PPTP VPN server, but as far as I know this KeeneticOS can set up also OpenVPN and possibly WireGuard, but as always PPTP is the easiest to configure. Start with logging into the box. It might sound obvious, but there are plenty of hardware which requires now unsuported algorithms and