Entering Fastboot mode on your Go to product viewer dialog for this item.
: Entering these modes can sometimes lead to accidental data loss if you select the wrong option (like "Format Data"). Back up your important files first.
: Once the screen is black, press and hold the Power button and Volume Up button at the same time.
: Release both buttons as soon as the Fastboot Mode screen or a boot menu appears.
On some firmware versions of the OPPO A58, you must enter Recovery Mode first to reach Fastboot. OPPO A5x – How to Enter Fastboot Mode