Questions :

My company has two ISPs providing WAN Conection.
Two Routers connect to these two ISPs, one WAN Link is selected to
route the WAN traffic ( this is preferred WAN Path ).
These routers have different IP addresses :

In normal working environment, the is selected to be the
Default Gateway for internet network.

Once the WAN Link of the Router with the IP is down, how
can I redirect the WAN traffic to the Default Gateway to the 2nd
Default Gateway automatically ? in order to make the internal network
has the redundant WAN service ?

My scenario my be the typical WAN redundant topology application.

Thank you