How we can configure DHCP relay on Cisco RV042 ? if both routers are on different ISP ?

Dear Muhamed

If you use the two ISPs as Primary and Backup, mean if one ISP fail the router activate the other WAN, the it should be no problem as there will be one DHCP server per ISP.

But if you use the two IPSs at the same time (Load Balancing), then i think the best way is that you configure your own DHCP server, and you can co-operate with your ISPs if you need to use there IPs.

I hope this help

Dear Muhamed please follow the detailed steps for IPv4 DHCP Relay Configuration on the following link

http://sbkb.cisco.com/CiscoSB/ukp.aspx?pid=2&vw=1&articleid=4256