SVN has no specific setup to user it over VPN.
This is just a generic VPN, possibly with a bit of port forwarding.
From the comments I take your office needs to set up a VPN server if they don't want to open the internal network at all.
SSH tunneling would be another possibility when ssh would be allowed.
If that VPN server is set up, you just install the VPN package with yum and place the config files that should be prepared by the VPN server admin (which might or might not be you).
"not having a firwall" at the office location probably means you have no open/fowared ports on the router.
When internal IPs for the office network are used and internet access is achieved through Network Adress Translation (NAT) you actually have a firewall.
You need to forward the VPN server port.
The VPN then needs access to the SVN server.
So either the SVN server is part of the VPN (or on the same server)
or you need another port forwarding on any VPN machine in the internal network (probably the server) to the SVN server.
You access the SVN server then with an address in the VPN.