Release the button once you see "Software upgrading" or a blue progress bar.
“The RSA7820 firmware update is generally safe you follow proper procedures and get the correct file from a trusted source. Most users see minor stability gains, but the risk of bricking or losing features exists. Only update if you are experiencing a documented issue the firmware fixes, or if your ISP requires it.” rsag7820 firmware upd
Turn off the display, unplug it, and open the back panel (if out of warranty). Locate the green PCB. You will see: Release the button once you see "Software upgrading"