This assumes you are familiar with the basic usage of the Gateway Migration Utility. Before you delete a private key from an API Gateway, you may want to list the private keys that are already in the API Gateway. Let's say you have a private key that has the following ID.

<l7:Id>00000000000000000000000000000002:key001</l7:Id>

Issue this command to delete the private key.

/path/to/GatewayMigrationUtility.sh restman
-host apig.example.com
-port 8443
-username john.doe
-password f5VPX0yUJPg.m4BrjdgMv84UgktddJD3xA
-method DELETE
-path '1.0/privateKeys/00000000000000000000000000000002:key001'

Or the -argFile option can be used, to reduce the number of options that are used on the command line.

/path/to/GatewayMigrationUtility.sh restman
-argFile example.properties
-method DELETE
-path '1.0/privateKeys/00000000000000000000000000000002:key001'

Something like this should be returned, which actually indicates that the private key was succesfully deleted.

Running..
Status: 204 No Content
Server: Apache-Coyote/1.1
Date: Thu, 28 Jan 2021 03:27:35 GMT