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It looks like the nut came off of the screw at the bottom of your circle. From one photo, it appears to me that the gear has then lifted up and no longer meshes with the rest of the gears in the system.
The mechanism to clamp a disc should not engage until some sensor at the back of the mechanism detects a disc has been pulled in and is in the correct location for the centre spindle to engage.
Can you actually see that highlighted gear turning without engaging the rack? I'd expect it to have a smaller pinion on the underside for that, rather than the upper part engaging direct; that's the bit the oncoming drive from the other gears connects to.
If I'm looking at the same screw thread as Gophert, I'd say that is attaching something to the chassis and the visible end is just excess thread beyond a threaded hole in the metalwork.
when I put the CD, it goes to right position. However,the mechanism (marked with number 1 on picture) needs a small hand help to put the mechanism (marked with number 2) on position. Without help, the mechanism stays near but not on position.
At some point, materials fail, mechanisms bind and the device is ready for the trash heap. The fact that the folded table has pulled out of position means any repair will be short-lived. You might want to consider a subscription to a music streaming service. I've been super satisfied with Spotify.