Following is very basic example: (This will return snapshots more than 90 days old across cluster)
PS C:\Users\Administrator> Get-NcSnapshot |?{ $_.Created -lt (Get-Date).AddDays(-90)}
Depending upon result, If you want to delete those snaps (older than 90 days), then you need to use 'remove-nscsnapshot' api, and if you don't want confirmation for each snap, simply add $flase:
PS C:\Users\Administrator> Get-NcSnapshot |?{ $_.Created -lt (Get-Date).AddDays(-90)} | remove-ncsnapshot -Confirm:$false
Side note: "remove-ncsnapshot" works in SVM context. So you need to make sure, you have connected to SVM before you can run that command, else it will complain APINOTFOUND.
Ex-
PS C:\Users\Administrator> Connect-NcController [SVM_mgmt_IP], not Cluster_Mgmt_IP.