Help needed to reset service indicator that has over-run the deadline

Hi there.
I did my own service on my 2007 CC but didn't reset the indicator afterwards. Now it is flashing and showing a negative mileage reading and won't reset using the clock button. Normally it would be a positive figure and then start flashing after the first push of the clock button. As it is already flashing, it won't follow the sequence.
Does anyone know how to get it reset now ? Thanks. Nev.
 
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