I suspect the plastic snapped on those two portions left and right. Maybe?

That’s one suggestion when fixing a plastic thing. If there was a brittle fracture (think silly putty when you rip it apart fast), then you’ll get this “distorted plane” surface somewhere. It’ll be smooth to the touch, not glossy, and its edge/profile won’t make sense as part of the design.

Why am I micromanaging your perceptions? Sorry. I mean look for spots where the plastic snapped.

If you find the corresponding one, the other half of that snap, it’ll fit perfectly like a puzzle piece. You can glue that. I think. It’s been forever since I’ve tried this. Might be you need to rough up the surface first, to ensure glue remains in the gap. Otherwise that brittle snap is too perfect and the gap volume is zero, meaning all the glue gets squeezed out.

I think. Again, over a decade since I’ve repaired any plastic thing, that I can recall at the moment.

Also, you could probably drill out some holes (probably wanna find some ancient greek style geometry trick to line them up. I suspect you could use intersecting lines to find the corresponding point on both pieces; definitely don’t eyeball it because the slightest misalignment in joining will make a ridge a person’s fingers or thumb can detect).

Anyway drill out holes on both sides that line up, and put a little threaded metal cylinder (screw with head and tip cut off) in. Make that join really strong. Probably better than just sanding it to make glue space.

Anyway if it didn’t brittle fracture, or if it came apart just not brittlely? Word? But ductilely, like silly putty pulled apart slow, then you’ve got a whole different thing. Probably gotta heat the plastic and re-form it. Talk to someone who does cars about reshaping plastic then.

Or maybe the little plastic nipple snapped and you need to replace it with a new one. It looks softer so harder to glue? Maybe?

Hope you enjoyed my rambling. Good luck. Who’s the action figure? Is that He Man?