For GUI, you can install: solaar, and pair/remove device to unified dongle.

https://pwr.github.io/Solaar/index.html

Pairing a logitech unified dongle with a device can also be done with 3 simple terminal commands

git clone https://github.com/treeder/logitech_unifier.git
cd logitech_unifier
sudo ./autopair.sh

Turn of your logitech product you want to pair, and press enter
Now turn the unit back on, and the unit should now be paired.

Source: Original article here
Github: https://github.com/treeder/logitech_unifier