Factory Reset Magic Keyboard (A1644)

Factory resetting the Magic Keyboard (A1644) can be done by following these steps:

1. If the keyboard is currently paired with any device, you'll need to unpair it first. On your Mac, go to System Preferences > Bluetooth. Find your Magic Keyboard in the list of devices, click on the "X" next to it, and select Remove.
2. Turn off the Keyboard: Slide the switch on the back of the keyboard to the "off" position. The green light should turn off.
3. Turn the keyboard back on by sliding the switch to the "on" position. Immediately, press and hold the Power button for about 5 seconds. The green light should start blinking, indicating that the keyboard is in pairing mode.
4. Now, you can pair the keyboard with your device again. On your Mac, go to System Preferences > Bluetooth. Your Magic Keyboard should appear in the list of available devices. Click Pair.

Ok, then try the following steps:

1. Slide the switch: Slide the switch to the “off” position.
2. Hold the switch: While holding the switch in the “off” position, press and hold the power button until the keyboard turns off.
3. Release and turn on: Release the switch and press the power button again until the keyboard turns back on.

If that doesn't work, sorry I don't have this keyboard to verify, then I suggest that you contact Apple Support directly for further assistance. To do so, simply select the "Support" link on the lower left-hand side of the forum's web page.