When you give up a shift, you are indicating that you don't want to work that shift if possible. Keep in mind that you are still responsible for working that shift until another employee has picked it up and the change has been approved by your manager.
Select My Schedules from the menu
Select the shift you would like to give up
Tap the Give Up button
Tap OK to give up the shift
Click OK to acknowledge warning
When a shift is given up, a red "Pending Give Up" box will appear on the shift until another employee picks it up and a manager approves.
After approval, the shift will disappear from your schedule.