Since official direct links for this legacy chip are often deprecated, you may need to use manufacturer-specific drivers or third-party repositories: Lenovo Support : Offers a Broadcom Bluetooth 4.0 Driver
If you managed to find an older .exe setup file but it refuses to launch: Right-click the installer file and select . Go to the Compatibility tab. bcm2035b usb bluetooth driver
This method is not for the faint of heart, but it can be effective when all else fails. Since official direct links for this legacy chip