Navigate to Assets /  Maintenance

Select the "Future / Preventative Maintenance" Tab at the bottom

Right click and select Add New Maintenance.

Begin to fill out the maintenance information.

Select the date to start tracking from.  Select how you are going to track the maintenance (Days / Distance / Volume, etc).

Enter your interval amount (not an odometer reading)

Make sure you select the "Recurring" check box.

Save and close.