How to disable Channel Type in HR Help Desk

Summary:

For HR Help Desk Requests, we would like to only have 'Email' and 'Web' as the options available in the drop down list.

Content (please ensure you mask any confidential information):

For HR Help Desk Requests, we would like to only have 'Email' and 'Web' as the options available in the drop down list, when creating a help desk request. We have not been able to successfully disable the other options. We need the steps to disable the other options as we have followed the steps in the implementation guide and the options are still showing up.

Version (include the version you are using, if applicable):