If it’s only a shim that’s stuck, it’s probably only a couple inches long. If it’s not too tight you could try tapping it down and folding in the shim. Or risk knocking it all the way down out of the shim and hope it doesn’t catch in the seat tube.
Alternatively you could try putting a longer bolt in the star nut and attach something on there that will let you whack it with a hammer to try pull it out. Just a bit of angle iron with a hole in would work.
Also keep in mind folding the shim in. If you can get the star but out of the way it would get that shim out really quickly
If it’s only a shim that’s stuck, it’s probably only a couple inches long. If it’s not too tight you could try tapping it down and folding in the shim. Or risk knocking it all the way down out of the shim and hope it doesn’t catch in the seat tube.
Alternatively you could try putting a longer bolt in the star nut and attach something on there that will let you whack it with a hammer to try pull it out. Just a bit of angle iron with a hole in would work.
Also keep in mind folding the shim in. If you can get the star but out of the way it would get that shim out really quickly