To remove a space bar, I remove the keys either side, and then very gently wriggle the space bar up by lifting alternate ends very slightly.
If yours is already raised on one side, that stabiliser has probably already popped out.
Do these have Costar or Cherry stabilisers? If Costar, you can put a bit of tape, or plastic sandwich bag, over the stem under the space bar before you reinsert the stabiliser insert - should stop it from falling out again too quickly.