So the problem is the model ? The model was acquired from a 3D scanner, converted from obj to dae then to gltf. If that is the problem then there isn’t much that I can do ?
No, that’s something totally different. Modulating metalness influences the actual property of a material’s surface. Using an environment map is a IBL technique which stands for image-based lighting. I suggest you google the topic since there are enough resources that explain IBL far better than I could^^.
The basic glTF example also shows how to apply an environment map to a model.