Plug your OPPO A74 into your computer via a USB cable.
Fastboot mode on the OPPO A74 is accessed by powering off the device and holding the Volume Up and Power buttons simultaneously, although some versions may require Volume Down. The device can be exited from this mode by holding the power button for approximately 10 seconds, according to guides on HardReset.info . Fastboot Mode OPPO A74 - HardReset.info How to Open Fastboot Mode on OPPO A74