3D model help


Can any 3D modelling types help me out please? I have created a model in .obj format using a Photogrammetry app but when I attempt to import it into Studio I get the following error message: “One or more meshes of this model do not have an indexed triangle list.”

Depsite trying to read around it, I am at a bit of a loss as to what this means or what I can do about it. I am a total novice in 3D, trying to find a workable way to create models from our existing physical resources to use within Studio.