However, the default admin password should be stored in read-only memory, which should be accessed when the modem is hard/factory reset (by holding down the reset button for 10 seconds). As it exists, a factory reset only resets the password to the ISP-modified value.
https://www.amazon.com/Motorola-MG7550-AC1900-Gigabit-Maximum/product-reviews/B01JGT2JI6

