Problem assigning static IP address

Hi I'm trying to assign a static IP address to a server on my network. Here is my setup, I have a sonicwall router which also does DHCP, with a software that runs on a dedicated server on site. I'm trying to assign a static IP address to that server but the connection is made through a VPN tunnel (managed by sonicwall as well), I'm trying to figure out how to assign an IP to this server instead of the VPN assigning it one of it's reserved range. I don't want to just connect the server through a regular switch because I don't know why it was setup this way in the first place, it was done by a professional and I'm not sure I'll be able to fix anything I break. Any help would be greatly appreciated, thanks in advance