- Stop all servers and close MAMP and MAMP PRO.
- Switch to the Finder, press cmd-shift-G (or select "Go to Folder") and type or paste "/Library/Application Support/appsolute/MAMP PRO/db/" and click "Open".
- Append "_bak" to the folder `mysql57`.
- Make a copy of the "mysql56" folder and rename it to "mysql57".
- Start MAMP PRO.
- Start the servers.
- Select "Upgrade MySQL Databases ..." from the "Tools" menu.
If databases are still missing, sorry. You will have to restore your backup!