Users who SSL-VPN into the office need to route to a different subnet which is connected via an IPSEC VPN

You should already have Address Setup for your SSL VPN Users and Address for Remote Site

Add the below polices

Policy :

Incoming Interface <VPN interface to Remote Site>
Source Address VPN all
Outgoing Interface ssl.root
Destination Address SSLVPN_TUNNEL_ADDR1
Schedule Always
Service all
Action Accept

Policy :

Incoming Interface ssl.root
Source Address VPN SSLVPN_TUNNEL_ADDR1
Outgoing Interface <VPN interface to Remote Site>
Destination Address all
Schedule Always
Service all
Action Accept
Enable NAT
Use Dynamic IP Pool and Create a pool (<IP of Fortigate>-<IP of Fortigate>).