Hey Miguel,
Here you have a step by step:
1. Download a full snapshot from the cloud environment and restore it locally in postgresql (https://docs.mendix.com/developerportal/operate/restore-backup-locally/)
2. Run locally the app and modify the data (or just delete objects directly through postgresql be careful with this approach to avoid data inconsistency)
3. In Pgadmin > Right-click on the modified backup > Click on 'Backup'
4. In the filename field enter 'example.backup' and hit the 'Backup' button.
5. Wait for the process to complete
6. Move the modified .backup data to the db folder on the original full snapshot folder
7. Compress the three folders (db, tree and .metadata) using 7-Zip. First compress the folders into a .tar and then compress again into a .tar.gz (gzip)
8. Upload the .tar.gz file to the Mendix app in Developer Portal
9. Restore it
I hope it helped!
Best Regards,
Ricardo Pereira
This could help you.
https://docs.mendix.com/developerportal/deploy/private-cloud-data-transfer/