Step 1. Download the latest build of Atmosphere and fusee-primary.bin here.
Step 2. Download atmosphere sigpatches from here (these enable you to run game dumps, and use homebrew NSP applications like Tinfoil. If the links opens like a folder, click the download arrow near the top right.)
Step 3. Extract the contents of atmosphere-X.X.X-master-XXXXXXXX+hbmenu-X.X.X.zip
to the root of your SD card.
Step 4. Open the fusee.zip
and extract the atmosphere
folder in the archive to the root of your SD card (these are the patches that enable atmosphere to load game dumps and homebrew NSPs.)
Step 5. Put your SD card back in your Nintendo Switch.
Step 6. Inject fusee-primary.bin to boot your switch with a payload injector.
Verify you're running Atmosphere by looking in Settings
-> System
and you should see Current Version: X.X.X|AMS X.X.X|X
if you see this, congratulations, you're running Atmosphere.