Nice first bowl. To renove the tenon make a jam chuck and bring the tailstock up to the tenon to hold it in place, make sure it is centred. Gently turn away as much of the tenon as possible and then remove the rest by hand. For future reference when you turn the tenon put a small dimple in the centre of it so when you come to reverse the bowl you have the centre already marked for the tailstock to go into.