I want to coonect those 2 lan's with a router , Is that possible ?
Yes, that is what routers do! If you already have gateway IPs configured then that implies that you already have at least one router (or device acting as a router) configured.
If these are actual LAN subnets then you ideally want to route all traffic through the gateways you already have configured.
A much less optimal solution would be to configure your gateway device(s) to send ICMP redirects instructing the hosts to route traffic through a different gateway IP (i.e. your new router) when trying to get to one of those subnets.
what are the modifications to do to my configurations
With no configs posted here, it's hard to say!