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. Press the Volume button to navigate and Power button to choose in order to select Fastboot Mode.
5. Fasboot Mode has started. It can be navigated with Volume Keys (movement) and Power button (selecting).