Unable to reset to factory defaults on XGS1930-28 with frontpanel reset

I tried reseting to factory defaults by holding in the reset button 7 sec, 10 sec, etc. in the frontpanel but with no success. (I did not use the restore button)

the customer does not have user and password for the switch.

I search how to "reset to factory default" thru Zyxel PDF on the switch and thru search engines, ChatGPT, zyxel horums but no solutions works.

Does this reset involve taking power and still hold in the reset button for a reset to work?

Hope some can point me to some official Zyxel documentation for reset to Factory defaults

Br. Jesper