In the vehicle's Edit form, under Oil change and service, set how often each is due by distance and by days, for example oil every 10,000 km or 180 days. Whichever comes first makes it due.
The Oil change and service column on Vehicles shows what is left, for example "Due in 2,300 km or 41 days": green when fine, amber when due soon (within 10% of the distance, at least 500 km, or 14 days) and red when due now. The Dashboard lists them, and Admins and the Fleet & Compliance team get an email once when it is due soon and once when it is due now.