As such the database move will drop the existing data. However for anything that is of interest, the old instance will be available until 2023-10-16 at:
From there you should be able to login, go to the section with the desired object (Dashboards, charts, datasets, saved queries), mark "Bulk Select" select anything that is desired, then export. On the new superset (available at
superset.wmcloud.org starting on 2023-09-11), go to the same section and push the import button (which looks suspiciously like a download button) and import the file that you exported from the old superset.