hi
you juste create default route to your main office trougth tunel interface and cretae policy source and destination example
if you use rout firewall for internet access and also for VPN
you can use source policy routing (PBR) first policy route use it only for Traffic HTTP and DNS "port needed " and scond source policy routing you use all traffic tunel.
or if your firewall is used only for VPN traffic you use route destination (destination based) with tunel interface 0.0.0.0 tunel.1 0.0.0.0.0
hope this help you