Accessing modems with mwan3

I need help to configure the firewall/iptables to access my two modems on the WAN1 and WAN2 side, with mwan3 enabled. These two modems have identical fixed IP With mwan3 enabled, I can force all traffic to this IP to one WAN interface in order to access the modem web page. DNAT only works with PREROUTING and OUTPUT. So I cannot use two distinct IPs for mwan3 rules then redirect designation IP to Any solution to access both modems together?