Right Phill lets get this sorted first a question will it fit over the bed bars if so put your chuck on the lathe fold up some a wad paper towel and place it over the chuck like so
Next find the centre of your recess then place the dish over the paper towel and bring the tailstock into play and trap the dish in-between the chuck and tailstock
Bring the tool rest up start the lathe not to fast at first and start to remove or reshape the foot with a spindle gouge turned on its side if you are going to remove it then leave the centre to be removed by hand of the lathe
if you want to just re shape the food then just put it back on your chuck don't over tighten it though start the lathe again slowly just in case the bowl has changed shape and is out of balance then rework the foot with a spindle gouge on its side and take light cuts
hope this helps mate its not that hard to do honest