Take over ownership of Dataflow Gen1 with REST API?

Hi bekkac579 
Thanks for raising this you've analysed it correctly. Power BI Dataflows Gen1 does not currently expose a public "Take Over" REST API like semantic models do, and Update Dataflow can't be used since it requires existing ownership.

The supported workaround we usually recommend is Export -> Import as the new owner:

• Export the dataflow definition (as admin or current owner):
  GET https://api.powerbi.com/v1.0/myorg/groups/{workspaceId}/dataflows/{dataflowId}​

  This returns the model.json.

• Import it while authenticated as the new owner (user or service principal):
  POST https://api.powerbi.com/v1.0/myorg/groups/{workspaceId}/imports?datasetDisplayName=model.json

  The identity making this call becomes the new owner.

• Reconfigure credentials and refresh schedule, then delete the original dataflow.

A few practical tips:

1. The new dataflow will have a new ID, so update any linked dataflows or semantic models that reference it.
2. We strongly recommend transferring ownership to a service principal or shared service account to avoid this situation recurring when team members change.
3. For bulk migration, this can be scripted in PowerShell or Python by iterating over GET /groups/{workspaceId}/dataflows.

Best Regards,
Cheri Srikanth
CST Team.