Any Idea ?
Any approach to take as an advice or suggestion before converting from string to memo or any idea on how to take the backup of db in Adobe Campaign classic.
If you're fully hosted with Adobe you can request a DB restore, IIRC they keep at least 7 days of full snapshots.
Past that contact your local IT dept for DB backups or mad scientist for time travel.
In the future check over the update wizard's DDL and if necessary use alter statements in packageable SQL scripts to change columns.