you are on windows ,right ?
pull out the sd card from gameshell, then insert it into PC, but DON’T FORMAT IT , windows will notice you that
the card can not be recognize blah blah blah , just ignore,
the use
balenaEtcher - Flash OS images to SD cards & USB drives
to flash the downloaded img file into the sd card
windows will assign the sd-card a new Disk character , like D: or else, just check it in the My Computer and remember it
be careful
in etcher, select the downloaded img file as source, and select the new Disk character as target drive
NEVER choose the C: ,it’s you windows system disk.
then flash it
after finished, pull out the sdcard from PC ,re-insert it into GameShell, then boot up GameShell
All done.
the whole process is just a Restore factory settings
good luck