Consider Educare. A client is VPN'd into E4, and can access everything onsite there. Howerver, they also need to reach the file server, which is at a completely different site. The folks onsite can reach it just fine, but this remote person cannot.
This is because of how the VPN works. By default, we build our Windows-based VPNs with something called split tunneling. That is, the computer will ONLY use the VPN for things it knows it can reach, aka, the local subnet. If split tunneling is off, then ALL their traffic goes over the VPN - streaming video, backups, Facebook, etc. Less than ideal for multiple reasons. However, as in this case, that means by default the only network reachable is the local one, and with the case above that's not what they need.
Powershell has a command specifically made for this setup: Add-VpnConnectionRoute.
The syntax is as follows:
Add-VpnConnectionRoute -ConnectionName "VPN Name" -DestinationPrefix 172.19.0.0/24 [-AllUserConnection]
ConnectionName is the name of the VPN in question, obviously. Quotation marks are a must because most have a space in the name.
DestinationPrefix is the remote subnet, including the mask. /24 is 255.255.255.0, /23 is 255.255.254.0, and /22 is 255.255.252.0 . (It's binary math. Ask for help if you're not sure because subnetting is its own weird skill.)
AllUserConnection is an optional parameter. Only use this if the VPN is installed at the computer level instead of a user level. You can double check this, and the name, by running the command Get-VpnConnection with and without that part.
Once you run the command, if the VPN is currently active, disconnect and reconnect it and try again.
In the above example, the VPN name is Educare VPN, server is at 192.168.136.2, the remote subnet mask is 255.255.255.0, and the VPN is an all-user one. So in this case, the command would be:
Add-VpnConnectionRoute -ConnectionName "Educare VPN" -DestinationPrefix 192.168.136.0/24 -AllUserConnection