Show private feedback to moderators

We have received a private feedback (in the Helpdesk), which shows to the admin as "Current feedback is visible only for owner and project administrators." My colleague, however, who has all relevant permissions (editing, moderation etc.) at "User settings and access rights" cannot access the forum and sees the error message: "This forum is private. You don`t have access permission for this forum."

How can I give the permission to our staff to operate the helpdesk?

Thanks!