I think that after each oil change or service, a dealership would use the diagnostic plug to check things, and, not having this check somehow causes the light to come on , that is what, I now think happens. As l have said there is a system connected to a second trip meter, if I left this as it is intended every 1000 km it would light up, for an oil check ,and I would have to reset it.

In my JoyMax manual it says

Engine oil indicator
Engine oil indicator is for showing engine oil inspection / replacement time. When the vehicle is ridden for approximately 5,000 kilometer, engine oil indicator illuminates which means engine oil inspection /
replacement is needed. Press “S” (Oil Reset) button to reset engine oil mileage. Engine oil indicator goes off when the “S” button is pressed and the engine oil mileage will be recalculated from the current riding mileage. Engine oil level should be checked every 1,000 kilometer and replaced every 5,000 kilometer.

Dunno if that helps or yours has anything similar?

In the case of the Cruisym300 the oil check light/trip meter is at 1000km. I do not need a reminder to check oil I do it weekly. I have been using the meter to do mpg checks, resetting it on fill ups. As I have now done 11000kms this means I have rest the meter many times. I just thought someone may have had a similar experience,but, the Cruisym is not that common, only being on sale in the UK for 12 months.