If you need to replace a damaged propeller on the Nano Drone, flip it over and take a look at the propellers. There are A and B markings on the propellers. Take a fork and place under the center of the propeller and lift up gently, slowly removing the propeller. Make sure to have the replacement propeller ready to go that matches the damaged propeller. Place the new propeller on the motor and give it a nice firm push. Don't push too hard... make sure the propeller can still spin freely, and you are ready to fly again.