Almost all models I publish on Sketchfab are under CC Attribution (CC BY) — check the individual model page to confirm. If it is, you're free to use or modify it for any purpose, personal or commercial. Just credit me as the original author.
"[Model name]" by Mark Peters is licensed under Creative Commons Attribution (CC BY 4.0)
Replace [Model name] with the actual title from the Sketchfab page. A link back to the original is appreciated but not required.