I am working on the App Customization Specialist Superbadge and this one has me baffled. Here is the part I'm stuck on...

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!".

Based on what I'm reading, they seem to be asking me to create a Quick Action button that creates a new record with the necessary fields set to default values. The problem is that two of the fields that are required are Lookups that I was required to create in the first challenge. One to supply the User Name and another to supply the Volunteer Shift Name. Quick Action default values can't populate Lookup fields, right? I tried creating a flow, but you can't trigger an autolaunched flow from a Quick Action, only Screen Flows. The challenge wants one button click and it's done. Can someone tell me what I'm missing here?