You can find the add-in under the OTHERS 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 "Cycloidaldrivesmaker_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

More information is available in the guide document.

If the plugin's icon isn't visible in Fusion, please run the add-in manually and check the Run on Startup option for the plugin on plugin's window:

Design workspace -> Utilities tab -> ADD-INS icon -> Add-Ins tab.

The second option for opening this window is pressing SHIFT + S.