Hi spring-onion,
thanks for your quick reply.
a) and b) worked. However, if I hold down the power button and press the volume up button once, it only switches from recovery mode to rescue mode.
When I press power on in Recovery, Rescue, or Restart Bootloader mode, the green Android mascot appears with "No command" underneath. After that, no button responds for 2 to 5 minutes. Then it boots again, or if I press volume down at the same time, the menu appears, and everything is back as at the start.
I can't find the 'factory reset' option at all.
The message "Device state: locked" worries me. How can I unlock the device?
The supplier of the device responded to my phone call today requesting assistance, stating that they would not be able to help until the New Year. Therefore, I am really hoping for your help.
I wish you a Merry Christmas in advance.
Best Regards
Rene
BTW: how one can set the post to unsolved?