Take a look at this...
Deleting a case - IBM Documentation
It documents a "1 at a time" manual process and caveats using in a Production environment.
There is also the option of resetting the test environment...
Resetting the test environment - IBM Documentation
In the end we developed a custom case solution that allows you to specify a set of cases to remove and provides "2 pairs of eyes" checking, a dry-run capability, etc. as none of the above options really worked for us and our customers.
Good luck!
Regards,
Dave.
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