If you get scheduled on a day when you can't work, you may be able to get a coworker to pick it up for you so you're no longer responsible for working that shift.
From the website:
To make your shift available for others to pick up, click on the shift to open the details. Then, click on the options menu (3 dots) at the bottom and select Make shift available.
From the mobile app:
Go to the Shifts tab and locate the shift in the list. Tap it to open the details.
From the shift details screen, tap the options button (3 dots) at the top right and choose Make shift available.
You'll get a confirmation message showing that the shift is now available for pickup.
Once your shift is made available, Sling will send out a notification to anyone else assigned to the same location and position as the shift so they have a chance to apply for it and take it over for you.
Whether you make your shift available from the web or the app, please keep in mind that you are still responsible for the shift until someone else takes it and/or a manager approves the swap.