Map Scale Zoom Control - lost settings

Hi

I used to be able to control the Map Scale from the stearing wheel but since the battery went flat(car left 6 weeks) I have been unable to do so, or work out how I managed to set this feature up in the first place! (old age causing memory loss?)

I cannot find any mention of this in the Columbus or Car Manuals.

Can anyone offer any advice as to how to restore this function?

Thanks in advance

Philip L Jackson