MetalKettle was a popular repository for Kodi add-ons, but it is no longer available. Therefore, it is not possible to install MetalKettle on Kodi anymore. However, there are many other repositories available that offer similar or even better add-ons than MetalKettle did. Here are the steps to install a repository on Kodi:
1. Launch Kodi and go to the home screen.
2. Click on the "Settings" gear icon on the top left corner of the screen.
3. Select "System" on the bottom right corner of the screen.
4. Choose "Add-ons" from the menu on the left.
5. Turn on the "Unknown sources" option if it's not already enabled. This allows you to install add-ons from third-party sources.
6. Go back to the "System" menu and select "File Manager".
7. Click on "Add source".
8. Select "None" and enter the URL of the repository you want to install. Make sure to enter the URL correctly.
9. Enter a name for the repository in the "Enter a name for this media source" field.
10. Go back to the home screen and click on "Add-ons".
11. Click on the "Package Installer" icon on the top left corner of the screen.
12. Select "Install from zip file" and choose the repository you just added.
13. Select the repository zip file and click "OK" to install it.
14. Wait for the repository to install and you'll see a notification when it's complete.
15. Go back to the "Package Installer" menu and select "Install from repository" to access the repository and install add-ons.
Note that the steps may vary slightly depending on the version of Kodi you're using. But the general process is the same. Also, make sure to use repositories and add-ons from trustworthy sources to avoid any security or legal issues.