Hi NiallConsidine,
Thank you for reaching Microsoft Community.
To make sure first: This is the mouse and keyboard that you have (Wireless Desktop 900 | Microsoft Accessories), correct?
If yes, Wireless Desktop 900 does not have any pairing button. There should be a USB dongle that comes with your Wireless Desktop 900. You can just connect the USB dongle to the USB port of your Surface Laptop Go and it should connect automatically.