XDA Developers is the most trusted source. Ensure the FTF matches your specific region and model (G3311).
Instructions on how to if you forgot your email.
Choose your preferred regional operator firmware from the list. Opt for a customized/unbranded variant (e.g., "Customized GEL" or "Customized International") to prevent carrier bloatware.
Turn off your phone. Hold the Volume Down button while connecting it to the computer via USB.
Press and hold the button until the phone vibrates to initiate the boot sequence.