Very old Bluetooth adapter/dongle on Windows XP: Plug the dongle into the pc. If it does not find the dongle and pops up an Add New Device Wizard, download:
https://dl.waspbarcode.com/kb/scanner/ERDBT.zip

Extract the ERDBT.zip, then choose the option as Advanced and browse to the location where you extracted the file. It will continue to install the Bluetooth drivers.