The Chicago screws are glued into the domed caps, and sometimes they can break loose. Find a pair of needlenose pliers with a long, thin nose and grab the shank of the screw between the button and the chap, then try to unscrew it from the underside. It takes some finagling.
Your buttons will be toast- you won’t want to use them again because the female part of the Chicago screw will continue to spin around and you’ll never get the buttons tight again.
Attaching brass Chicago screws insidethe domed aluminum button shape was a challenge. The two dissimilar metals did not play well together with any glue or welding system we ever tried… and we tried just about everything. Regular old sticky snotty chap glue- a puddle of it inside the button mold- worked better than anything but sometimes if they got over-tightened the glue would let go, and sometimes, after years, they just let go too. We never found a more reliable way to attach those screws.