You can live migrate data from existing MongoDB deployments monitored by Cloud Manager or Ops Manager into Atlas using the live migration service through the Atlas UI.
To locate live migration (push) in the Atlas UI, in the left-side panel of your organization's page, go to Live Migration to Atlas and select Migrate from Ops Manager or Cloud Manager.
Cloud Manager or Ops Manager pushes data from the source replica set to a destination replica set in Atlas.
Cloud Manager or Ops Manager pushes data from the source sharded cluster to a destination sharded cluster in Atlas.
Live migrate a standalone MongoDB node