Migrating reports and datasets to a different workspace

We have a workspace that consists of dataflows, datasets, and multiple reports that connect to those datasets.  Recently, it was determined that one of the datasets and any reports connecting to it need to be moved to a separate workspace for security purposes.

I can't remove all members from the current workspace because they need access to the dataflows, which requires workspace Member access.  Unfortunately, this gives them read access to this particular dataset that we're trying to migrate.

I am able to save copies of the reports in question to the new workspace.  I am also able to download the dataset in question's PBIX file and re-publish that dataset to the new workspace.  However, I cannot figure out how to point the copied reports to the copied dataset.  The option to download the reports' PBIX file is greyed out, this might be because the reports were all created directly in the service instead of Power BI Desktop.  I have Admin access to the workspace, so I don't think that's the issue.

I feel like I must be missing something really simple here.  Any ideas?