Gently lift the cup away and peek inside without fully removing it. You should see the following:

A thin layer of tape holding a cable going from the boards to the NFC antenna in the outer shell piece.

In this picture it's already unstuck.

Another thin layer of tape below it holding the headband cable and NC microphone cables to the mainboard.

Gently pry the layer of tape holding the NFC cable.

This area has three layers of tape on top of the circuit board - make sure you're only unsticking the top layer that is holding the NFC cable for now.

Once you've done that, it should have enough slack, and then you can open it like a book from the right side.

You cannot disconnect the NFC antenna cable unless you have a soldering iron. Be careful if you are doing any further disassembly to the Left Speaker.