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Juniper-wool posted on r/hondafit3w
https://youtu.be/PtxW3iaFihw?si=_8Hf7AqDMCL5Ap0V&t=172 between 2:50 and a couple of minutes on, you'll see how to disassemble the door panel, and the door lock controller is fastened with 2 or 3 screws. Disconnect the contact to the controller and install the new one. This one should fit your car: https://www.amazon.com/SWITCHDOCTOR-Window-Master-Switch-2009-2014/dp/B00SCBL8RI