Remove the bowl from between centers. Now remove the tenon on the bottom by sweeping the sharft of the tool across bottom of the bowl. You could use a chisel but that requires finding a place to sit the bowl and hold it steady so as not ot be pushing sharp tools at your hand. Keep it simple.
Similarly, cradle the bowl in one arm while removing the inner tenon by striking it with a mallet or, my preference, the handle of the last tool I used in turning which is likely the same one I used to remove the bottom tenon. Give it a good rap. If the tenon does not pop off the first time rotate about 90° and try again. If at first you don't succeed and all that.
Treat the end grain of the bowl with Anchorseal or its equivalent. This is a wax emulsion designed to slow the drying of the bowl blank and reduce cracking and splitting. Some people bury the bow in damp shavings or put it in a couple of paper bags instead. I do not have paper bags that big and find that damp shavings promote mildew and mold. Your mileage may differ. Use something. I prefer Anchorseal I also find it more than sufficient to just treat the endgrain on the outside of the bowl. Again, it is your bowl. Go ahead and paint the whole inside and outside if you like. I find just painting the outside endgrain to work really well.
Here are the other results of a bit of fun and work. If your idea of fun is a pile of shavings after a bit of time at the lathe, this should look pretty good. This is just from the one bowl roughing. Next step for it is likely the compost pile.
The newly treated roughout can not now join a few of its friends as it waits to dry and be finish turned. I find that three months is about right in the shop until the bowl is ready to be finished but some of these have been sitting five years, maybe more. Since there are generally from 75 to 100 bowls waiting, I do not turn them in any particular order, just whichever suits my fancy.