When a label is assigned to VM(s) (or Host, Datastores, etc.) then you can use the label name or label values in search query. There's an example of "Department" label:
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You can filter out VMs by typing this Search Queries:
Department:Finance
Department:*i*
Or you can use just label value, i.e. "Finance" as a SQL query.
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For further information visit SolarWinds VMAN Admin Guide and and search for "Custom Labels".
