There's 2 ways to schedule these: from the Agreement tab or in the Call Taking feature.
Tap the Agreements tab from the Dashboard and then choose Maintenance Due.
Here you will be able to view your customer information as well as their agreement information. Customers that have Maintenance visits due, that have not yet been scheduled, will have a SCHEDULE button in the Job column.
Clicking on this will open the Call Taking feature, which allows you to get that visit scheduled.
Not sure how to use Call Taking? Find out how HERE
Tap the Call Taking button and choose your customer.