@Amr_Ali I believe the following two links should assist you with this.
The mechanism that you most likely want is called ECMP and should allow you to distribute connections across two different ISP connections.
It sounds to me like you're looking for classic link load balancing. So.. do you want outbound link load balancing or inbound? Here's how it works with LTM / DNS:
Inbound: set up a WIP in DNS for each service. Each SP has a VIP. (btw, you can accomplish this with F5 XC Cloud managed DNS and LTM. don't even need DNS license for that.
Outbound: Set up aa all-ports forwarding VS on the inside leg of your LB. The pool for that VS has each router's GW as members. Set up persistence as you like it.. source / dest.