I am stuck on challenge 3. I am trying to create a ACTION Volunteer Shift Object. Requirements are 
"Quick Self Sign Up
Maria asked for a quick way for users to sign themselves up for a Shift directly from a Volunteer Shift record. Your solution was an action with the label Sign Me Up. To keep it simple there should be no fields on the pop-up. Instead the action automatically sets the Volunteer to the user clicking the button, changes the status to Confirmed, and assigns the currently viewed Shift as the new record's Volunteer Shift. Once the action is done show the friendly message "Congratulations, you are signed up!".

Now When I am trying to select Staus field it does not show any of the Voulnteer Shift Worker fields to choose. FYT There is a MasterDetail Relationmship between these two. Volunteer Shift is the Master Object.