Download the .aip plugin file and place it in the Illustrator Plug-ins/Extensions folder. Access: Open the interface via Window > Mesh Tormentor .
If you want a on improving mesh workflows in Illustrator, I can write that fully – just let me know.
Ensure you download the plugin from a trusted community source, as the original developer site (Yemz/Vectorboom) is often reported as down or inactive.