Use the twiddly wheel on your BC stalk to scroll through the BC functions until the MOT symbol is displayed on the little screen. Press and hold the button on the end of the stalk for a few seconds, it may ask you if you want to reset (I can't remember off the top of my head), then you get the month and year for its next renewal displayed.
Press the button to select the month, use the twiddly wheel to change it, then press again to set. Same for the year.
Don't you have a handbook with your car?