You can find the add-in under the GEARS panel in SHWIVEL tab of DESIGN workspace. 

For creating gears, you must run this add-in. The window has default parameters, so you don't need to set them at the start.

Install:
1.Download the installer from Autodesk App Store.
2.Right-click on the "Downloads" folder and select "Open in Finder".
3.Right-click on the "Geartrainsmaker_macos.pkg" -> "Open With" -> "Installer".

Uninstall:
You can unload the add-in without uninstalling it by clicking the "Stop" button when the add-in is selected in the list box on the "Add-Ins" tab of the "Scripts and Add-Ins" dialog.
Unchecking "Run on Startup" causes the add-in not to be loaded in future sessions of Autodesk® Fusion 360™.
- Navigate to the ./ApplicationsPlugins folder and select the app bundle you want to uninstall
- Either drag the app bundle to the Trash or right-click and select “Move to Trash”
- Right-click on the Trash-Can and select “Empty Trash”
- If you prefer keystrokes, you can also just select the app bundle and then hit Command+Delete to move the app to Trash, then empty the Trash and the app will be removed

https://www.shwivel.com/faq