1. download https://github.com/winterheart/broadcom-bt-firmware/blob/master/brcm/BCM20702A1-0a5c-21ec.hcd
2. read https://wiki.debian.org/BCMHybridBTFirmware
3. sudo cp BCM20702A1-0a5c-21ec.hcd /lib/firmware/brcm/
4. [re]connect Bluetooth USB Dongle