To open on a Samsung Galaxy A7 (often referred to as Bootloader Mode in modern Android versions), you generally need to navigate through the Android Recovery menu . Note that most Samsung devices use Download Mode for firmware flashing, but you can access the fastboot interface via the following steps: Standard Method (Via Recovery Mode)
If your specific model has a (older A7 versions), press and hold Volume Up + Home + Power together. how to open fastboot mode on samsung galaxy a7 repack