Before you can use a Bluetooth keyboard, mouse, trackpad, or audio device, you need to “pair” your Mac with the device.
You need to pair your Mac with the device only once. The device remains paired until you unpair it.
Make sure the device is turned on.
Choose Apple menu > System Preferences, then click Bluetooth.
Select the device you want from the list, then click Pair.
If you are prompted on the device, click Accept.