See the notes on the Launcher wiki.

NOTE: The steps detailed below are not currently implemented.

1. Open the Fabric download page.
2. Click on “SKCraft Launcher” and pick your game & loader version.
3. Click the button to download the loader JAR.
4. Place this jar in the “loaders/” folder inside your modpack folder.
5. Test the pack and check the build logs for any warnings. If the game launches with Fabric running, you're set!