Sometimes there is a conflict between Scratch and the way Windows automatically connects to a bluetooth device that your computer has connected to before. To get around it, you have to manually tell your operating system to "forget" the device.
To "forget" the device:
- Open settings by opening the Windows menu and choosing Settings (the Gear Icon).
- Choose "Devices."
- In the list of device "Other Devices" click on your device and then click "Remove Device."
That should make the device discoverable by Scratch using Scratch Link.