Logitech K780 Frequently Asked Questions Manual page 27

 +Re-pair a Bluetooth device to the K780 keyboard
You can easily re-pair a device with your K780 keyboard. Here's how:

On the keyboard, press and hold down one of the Easy-Switch buttons until the status
light starts blinking.
The keyboard is in pairing mode for the next three minutes.

On the device, see
 +Manually select the operating system for the K780 keyboard
The Logitech Keyboard K780 includes an OS-adaptive key that has different functions,
depending on the operating system of the device you're typing on. Your keyboard can detect the
operating system of the device you're currently connected to. It automatically remaps keys to
provide functions and shortcuts where you expect them to be.
If the keyboard fails to correctly detect the operating system of your device, you can manually
select the operating system by pressing one of the following function key combinations for three
seconds:
Mac OS X and iOS
Press and hold for three seconds
Windows, Android, and Chrome
Press and hold for three seconds
 +Connect your Logitech Bluetooth device
Connect your Logitech Bluetooth device.