In the initial application, you captured data about the applicant and the e-mail address of the physician that has agreed to shadow them. For the physician to approve this, you'll make a second application for that physician (or more likely their aide) to use.
Create a new application form. In its properties, Application type must be VSys Live application, Usage must be External approval of existing application via URL.
Place any fields you want onto the application. In most cases you'll stick with user fields, but you can also put read-only fields about the volunteer/applicant such as their name or custom fields.
You can place the Status field on this application to let the physician directly approve or reject that original application; if you do, you should right-click on the field here and use Limit visible options to restrict the physician to only those statuses you want them to use.
Don't put any links to this application in VSys Live menus: this application only works when it's being used as part of a reference check.
Save the application.
Never put any private information about the volunteer on this application, or allow editing of fields that you wouldn't want edited by the physician. Anyone with access to the link in the generated letters could view and/or edit those fields!
The VSys tech support folks will happily give you a sample template to start with if you want.