[REQUEST] Reduce a high polygons model

Hello,

I'm far from being a modeler, I'm just a simple gamer who is looking to improve adding content to the game (modding GTA V to be precise).

I wanted to import this helmet model that has been kindly shared to the community: Shoei Neotec2 motorcycle helmet

But I have a problem: the model is a kind of "scan" and therefore has several MILLIONS of faces (and is therefore impossible to import in game). My goal is to get down to the minimum number of faces without losing quality (about 5000-6000 faces). One person has already succeeded in doing this but keeps it private.I have already tried but each time the model "breaks": the curves break into thousands of peaks.

I wanted to know if someone has already done this kind of thing?
Thanks in advance !