For security purposes you cannot reset the admin credentials without entirely wiping the machine.
Wiping the machine is done by what is called an Altboot.
So you would take the printers latest firmware version which is here.
Download and extract the dlm file out of the zip file.
The altboot process is simple, but we are not allowed to post the directions here, but other sites certainly post it. (See the GP9 link)
When the process completes, it will be entirely wiped, it will have deleted every single setting ever applied, so you will need to set it up from scratch. Expect the altboot to take anywhere from 20-90 minutes.
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