From this detailed guide, you can learn how to install 2nd Gear Build On Your Kodi.
2nd Gear is an extremely lightweight, quality build choice for streaming Movies and TV Shows in high definition. It uses the only One The Gears Kodi addon to provide on-demand media including 1080p & 4K definition..
this installation guide applies to all compatible devices including Amazon Firestick, Fire TV, Android & iOS, Mac, Windows, Android TV, Android Boxes, etc.
How To Install 2nd Gear Kodi Build.
- Open Kodi
- Be sure to have the Unknown Source box checked as Kodi requires this before installing 3rd party add-ons.
- HOME Screen > Add-ons > Settings button 
> Add-ons > Enable Unknown Sources.
- From your Home Click Settings (cog icon top left)
- Click File Manager
- Click None
-Type in the following EXACTLY https://zaxxon709.github.io/repo
- Click OK
- Click back on your remote/keyboard
- Click Add-ons
- Click Install from Zip File
- Click repo
- Click repository.709-x.x.zip.
- Wait for Add-On Enabled Notification
- Click Install from Repository
- Click The 7o9 Repo
- Click Prorgam add-ons
- Click Install
- Wait for Add-On Enabled Notification
- Click Close
- Click Yes
- Select 2nd Gear Build - > Install (Fresh install)
- Click Continue
- The build will now download and install. Once completed select OK to force close Kodi
- Restart Kodi and leave it for a couple of minutes to allow all updates to complete.