How do I only use arms of the mannequin for the first person camera view?

how do I create another instance of the model and only the arms that I can use

If you just want the arms, add the First Person Template content pack to your project, it has the arms separate from the rest of the mesh.

u have 2 options, create an example project of a first person shooter (already include in the engine) or a third person project (or in any case, a blank project with your own assets), and set the camera in the head, and move the arms towards the camera, and animate from there