Your Intel® NUC Kit 5i3RYH has a wireless-Bluetooth card inside. Before pairing your keyboard, I recommend you to update the drivers of your NUC, start with the chipset driver and Management Engine driver then, continue with the rest of the drivers.
Steps to connect the Bluetooth keyboard:
-Right click the Bluetooth icon available on the lower right side of your display
-Select add a Bluetooth Device
-In your Keyboard, 1) Turn it on, 2) Press and release the Connect button (bottom of keyboard)
-Your NUC will detect the keyboard, select Pair (On PC) and type the code (numbers) using the Bluetooth keyboard. The NUC will start the synchronizing process (It usually takes 2 or 3 minutes)
-The Keyboard will be up and running