Ducati Multistrada 1200 2016 Owner's Manual page 166

Day two-digit value starts flashing.
Press button (1) to decrease day value by 1 unit: 31,
30, ... 01, 31.
Press button (2) to increase day value by 1 unit: 01,
02, ... 31, 01.
Once you reach the value to be set, press button (4)
and the set day will stop flashing.
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