I'm in the process of merging two AGOL organizational accounts into one. Some of the data in the source org is owned by a consultant that they have added to a group as an external member. The data they have shared/published will ultimately belong to my org and will need to be migrated to the new target org. Does anyone know if there is a way to change the owner of those data sources so they can be migrated to the target org?
I think the good practice is to store a copy of the for the organization, in a file geodatabase and then add it into your AGOL account, as this will ensure you have a copy of the data that is controlled by your organization., and allows you to make edits or manage data security.
If you do have access to both portals, you can also have a look at this ArcGIS Online Assistant (esri.com)