: Reset the controller by pressing the SYNC button once (usually a small button on top or back), then press any other button to power it back on.
The system will check for updates and install them one by one. Do not disconnect the controller during this process. Method 2: Manual Update via Windows PC n-sl wireless controller firmware update
If you are using a Pro Controller (which uses a similar firmware base to Joy-Cons): : Reset the controller by pressing the SYNC