Enable candidates to select and work shifts of their choice.

Step 1:

Select Candidates from main menu.

Step 2:

Click on a candidate (You can pick any candidate)

• Select "Profile" tab
• Look for "Available Jobs" in secondary tabs and click on it
• Hit the button "Customize how Candidates view and interact with shift jobs"
  

Step 3: 

In setting popup click on option " Requesting to work and accepting shifts"

• Find the setting "Candidates can self assign themselves to shift jobs" - Enable it
• Save the changes.

Result:

Candidate will be able to see "Accept Job" button for a shift job on "Available Job" tab