Aborting an asynchronous replication failover is supported during the first phase of graceful failover when the protected data is read-only on both peers. The duration of this stage depends on how much data needs to replicated before changing the direction of replication.
Aborting Failover from the VAST Web UI
On the peer where you initiated failover, on the Protected Paths tab in the Data Protection page, open the Actions menu and select Abort Failover.
If the option to abort the failover is not present, this is because the process is advanced beyond the stage when aborting the failover is supported. If you wish to reverse the failover, wait until failover is complete and then run failover again from the new destination peer.