Connection to SQL Server over VPN

Get VPN connection IP address from IT server administrator
Set up VPN and login
Connect to SQL on local PC using SSMS or Visual Studio using SQL Authentication login and password
The server name to use in SSMS will be an IP address on the Network that you have used VPN to get to. You may or may not need to add \InstanceName.
It is not uncommon for this internal IP address system to be 10.0.0.x where x is the computer number
So format may be 10.0.0.x or 10.0.0.x\InstanceName

Special Cases
If the VPN internal IP address system uses 192.168.1.x then be careful that your local PC is not using 192.168.1.x
If it is then need to change the local PC IP address system to use 192.168.0.x

See Change IP address of a local (home) pc