How switch divert traffic to standby ASA when link to active ASA is down? Active ASA and standby ASA communicates through failover link. If active ASA detects its interface to switch is down, then it tells the standby ASA and the standby ASA becomes active. How does the switch connected to both ASAs know to divert traffic to standby ASA which becomes active after the interface to the original active ASA is down? Any required configuration on the switch?

Switches only forward frames based MAC address. The secondary ASA takes over the MAC address of the failed ASA.

Cisco has an explanation of the process.