Jay
Unless the previous owner used CA or epoxy to glue the mast base into the base fitting, it should be easy to wiggle out of the base fitting. If it is bonded, using care you can heat the area with a hair dryer or heat gun -
being careful not to over heat that area. I have used the tip of soldering iron on things like this. If you opted to try that you'd touch the tip of the soldering iron to the mast as close to the base piece without touching any plastic parts. Again,
be careful not to over heat the parts. I use undo the two screws that hold the base plate to the deck you should be able to determine if anything has been bonded together. If not with it loosen it might be easier to attach the problem.
The mast is held in place by the shrouds and backstay, so those would need to loosened or disconnected (sorry if that seems obvious). The manual instructs the builder to bond the mast pieces together so if that was done - your mast is one long piece now. Makes it a real pain to ship the boat to anyone if you want to sell it.
I'm hoping the guy didn't get carried away with the epoxy and bonded the mast to it's base plate. It should just be sitting in that little black base fitting and
should come out of there pretty easily. CA doesn't hold to ABS as well as epoxy in my experience - These would be the 2 most likely adhesives someone might use.
If he did, a little heat and gentle but firm wiggling should get it free. Good luck!
If you have the manual look at pages 7 figure 16 and page 15 and figure 33 - They show how the base plate is attached and how the mast just slips into it. The rigging holds the mast in place - shouldn't be bonded -