In the mobile app, Approvers can set reminders so that they don't forget about approvals waiting for their decision. They will then receive a push notification according to their respective choice.
This is how you set a reminder:
Click on REMIND ME at the bottom of the respective request in your "Decision required" section:
Select when you want to be notified:
As soon as the selected time has elapsed, you'll receive a push notification to remind you: