Factory Reset with old Parental Controls on?

Need to factory reset my old 7” Kindle Fire HDX (3rd Gen, model C9R6QM), but still have old parental controls set up on it from when my mom was rather touchy with how my brother and I used technology. Neither of us have any idea what the password might be, but need to factory reset it before I try to sell it.

Anyone have a way to wipe it clean without a PC password?