How to connect to the database via VPN?

Question

PHP

Clients have a base on postgres, on their local grid. We are blowing on a site written in php, taking and writing data there. Of course, they just couldn’t connect just like that, because. their ip is simply not even pinged, it's an internal mesh.
And now the admin writes that he opened it there and
gave a new address - no longer ip, but a domain
, and then writes
"pptp connection
Get an IP address XXX.XXX.X.XXX. Inside the tunnel, access to the server XXX.XXX.XX. XXX"
The last ip is just the ip of the server with the base.
Here's how I can connect to the database through php in this case?