False message about needing oil change

[Ms_Jam]

I recall seeing something about this on the forums. But now I cannot find it.

My Focus LZ is showing a message demanding an oil change every time I start up. It had the annual service about a month ago, so I doubt this message is correct.

In any case the very same thing happened last year. I took it to the dealer and it was fixed in a minute.

However, I don't want to spend the time going out there again. So does anyone have a reference to how I can fix it myself?

(I suspect the problem is that the servicing is happening before the anniversary of the purchase, and that the vehicle's software showing the message is triggered by time.)