Docker can be pretty complicated to administer, and there’s a lot of things that can go wrong.
I’m hesitant to provide specific suggestions without knowing much more about your server and Zammad deployment, and whether you can potentially restore from backups
Option 1 would be to reach out to a local IT support company in your area and ask for assistance, depending on your level of expertise.
Option 2 would be to consider migrating to cloud hosted Zammad. That way you get access to dedicated support, and the Zammad team will assist with importing your data: