I have received a .mtl & .obj file of the brand (smart-watch) from client.
Can I open .mtl in flame ? I doubt - what is the workaround ?
.obj opens but texture is missing.
The MTL files in NOT an image file. It is a metadata file containing information about the materials. It may reference image files but the media is not embedded in it.
Your best bet is to import the model into a 3D app with the MTL data and export the model with a baked texture. This should give you an image file that should correctly map around the model when imported into Flame.