On your Firestick home screen, go to Settings
Select My Fire TV
Select Developer Options
Turn on Apps from Unknown Sources
Go back to the home screen and select Search
Search for the Downloader app
Select Downloader and install it
Open the Downloader app
Allow any requested permissions
In the URL field, enter the official Kodi download page address
Download the Kodi APK for Android
Wait for the download to finish
Select Install
Open Kodi after installation completes
If prompted, allow any required permissions