To install the Steam app on your SHIELD TV home screen, open the NVIDIA Games app and select “Set up GameStream” from the My library row.
Make sure to login with the same account on both SHIELD TV and GeForce Experience (on your PC).
Next, select GameStream from the My Library row and launch Steam (Steam will show up as long as Steam is installed on your GeForce PC).
The Steam app will now be installed on your SHIELD home screen in the Games row.
Launch directly into Steam Big Picture on your GeForce PC from this app.