As per our content policy (https://sketchfab.com/terms#ip), in order to remove models from our site we require specific information from the owner of the copyright or someone who is authorized to act on the rightsholder’s behalf. This requirement flows both from our legal requirements and our attempt to avoid confusion around take-down complaints.
When completed, you will receive an email with a fully formatted DMCA take-down request that you need need to confirm and forward onto us at DMCA@sketchfab.com before we process it. Of course, if you already know how to write a qualified DMCA takedown notice, you can also send it directly to DMCA@sketchfab.com.
Note that this is a legal process; be aware that abuse can have legal consequences.