1. Hi. Start by turning off the phone. To do that, press and hold the Power button.
2. When the phone is turned off, press and hold Volume Down and Power button for a moment.
3. Let go of these buttons when an Android image shows on screen.
4. Choose Fastboot Mode by pressing the Volume Up button to scroll and Power button to select.
5. Superb, you are now in Fastboot mode. Navigate this mode using Volume Keys; select options with Power button.