How Can I Set Dynamic Detect a Specified Destination

Hi,

I have foritwan devices and four ISP. Sometimes, the one of our ISP can't reach our destination IP. I want to set fortiwan frequently ping our destination IP from each ISP port. If the one of my ISP can't reach our destination IP, Fortiwan won't use this ISP to reach our destination IP. It's better, if fortiwan can choose route base one the latency of ping. Could anyone tell me how I can set for my requirement? I can't find related configuration on fortiwan guide.