Required Linux,VPN freelancer for PiVPN - Access remote LAN devices from VPN job

We are using Raspberry Pi's in our water treatment plants to monitor the status of the equipment in real time. The Raspberry PI's are working fine.
Our next step is having the Pi's act as VPN so we can upload new software to the connected equipment remotely.
We can have been able to install PiVPN and connect to the pi remotely from our office without a problem we aren't able to access the other pieces of equipment on the LAN remotely. We would like to be able to communicate with that remote equipment so we can update software in real time.

This seem entirely possible but we are still having issues accessing the remote equipment.

Skills & Expertise Required

Linux VPN