I recently cleaned my spacebar and a piece is stuck I have taken off my spacebar from my MacBook Pro mid-2012 and now one of the plastic rotating things is stuck to the keycap, while the other is still in the key space. How can I get the thing stuck to the keycap off the hook?
The scissors are quite delicate - you might need to buy some replacement parts or a used / damaged model and harvest parts. Without a very detailed picture, I can offer general advice.


Look for hinge pins that are sheared off.
Get a scrap part from a similar model (keep in mind - keyboard revisions are quite possible on very similar models in time - a mid year bump can have changed physical keys - especially hidden under the black parts)
carefully examine the function of the pins, the spacers under a bright task light - dim lights and lack of magnification can easily let you miss a sheared part or other damage bending of small metal and plastic parts.