SDWAN Failover over Separate VPN Tunnels

I am new to FortiGates and need a little configuration help. We have two FG200F's at our datacenter as the firewalls and some remote sites that are using FG40F's and are connected via VPN. What I want to do is have two WAN's, one as primary and one as a failover. I need all traffic that is destined for our network that is traversing the VPN to swap VPN's in the event of a fail over. Not sure how that configuration looks.

Current set up is 1 WAN to remote site, VPN connect back to our network.