To dismount a snapshot use the
Dismount-PsbSnapshotSet cmdlet. Get the MountID from the List the Snapshot Set Mount History cmdlet.
The example below will remove the mount from the computer declared in
-ComputerAddress.
Dismount-PsbSnapshotSet -VCenterAddress $vcenterendpoint -VCenterCredential $vcentercredential -FlashArrayAddress $FADNS -FlashArrayCredential $FlashArrayCredential -ComputerAddress $vmname -ComputerCredential $vmcredential -MountId $mounts[0].mountid