In order to invite a Hiring manager to view the candidates in your project, they will need to have either an active Pro license or "Collaborator" license. If you need to add collaborator licenses to your account, please reach out to your account manager.
Afterwards, this can be done by going to the “Project Details” tab in your Project. You can invite other hiring team members or hiring managers by adding their email addresses under "Invite Hiring Team" or selecting from the drop down.
Also, please keep in mind that collaborator users can only view and qualify candidates who are a "Good fit" or "Not a good fit" and cannot make any edits to the search parameters.