Once the Fastboot Mode logo or text appears on the screen, release both buttons.
If your hardware buttons are damaged, you can use from a computer to force the device into Fastboot. how to open fastboot mode on oppo a37 verified
You will now see a screen indicating you are in Fastboot Mode. You can navigate options using the Volume keys and select them with the Power key . Alternative Method: ADB Commands Once the Fastboot Mode logo or text appears