Open MRT Key software just select on model Y83 then tick on Format unlock, and press the start button, just insert the USB to the phone switch off no boot key needed, and wait until the software says it DONE,
Disclaimer: Flashing firmware is not without any risks.
If you don't do it properly, you might render your phone inoperable.
If you decide to proceed we won't be liable for whatever might get wrong "neither we could provide technical support" just leave a comment or contact us on our google mail.