If, for any reason, you need to undo the data migration, you may do this via your Settings tab.

Click the "Undo" button and confirm your Import ID to start the undo process.

If your migration is still in process and you wish to stop and undo the results, you may click "Stop migration".

Then you may select "Undo Migration" (or you may opt to "Resume" to continue the migration where it left off).