MeshLab is an open source system for processing and editing 3D triangular meshes. It provides a set of tools for editing, cleaning, healing, inspecting, rendering, texturing and converting meshes. It offers features for processing raw data produced by 3D digitization tools/devices and for preparing models for 3D printing.
When your mesh is ready to upload, go to Filters → Smoothing, Fairing and Deformation → Export to Sketchfab. A pop-up will appear for you. You'll want to enter your API Token in the Sketch Fab Code field, as well as a title, description, and appropriate tags.
In most cases, we would recommend you keep Auto Rotate enabled.
Then, click Apply and your model will be uploaded to your account.