If you have made arrangements for someone else to take your shift, you can offer it to them in Sling and avoid another employee grabbing it before they have a chance to.
From the website:
Click the shift you want to offer, then click the options menu (3 dots) and choose Offer shift.
You'll get a prompt to choose the employee who will receive the offer.
Click Offer and the employee you choose will receive a notification to accept or reject the shift.
From the mobile app:
Go to the shifts tab, then find the shift you want to offer in the list and tap it to open the details.
Next, tap the options button at the top right corner and choose Offer shift.
The next screen will bring up the employee list. You can choose one from the list or type someone's name in the search box at the top.
Once you've chosen someone, you'll get confirmation that they have been sent a notification of the offer.
They will have the option to accept it or reject the shift. Your manager may also require approval for the swap, so keep in mind that the shift is still your responsibility until the exchange is approved.