As above, depending on how accessible the crown race is, you can either tap it up and out of the way with a flat bladed screwdriver and hammer, if there's nothing to hit, you may need to use a Stanley blade or similar to start the process, moving it up slightly until you can get something more substantial in there to lift it up and out.
You'll also need something to fit the race back on, I would not recommend a screwdriver and hammer for this as you could easily damage it. You can use plastic pipe of the correct diameter over the steerer tube. If you've not got anything I have found you can use a spanner with a larger diameter than the important part/lip of the crown race, but you have to be accurate and gentle.
Best to have the right tool of course.