Note: Samsung devices use "Download mode" (Odin mode) rather than Fastboot. Below is a detailed, step-by-step guide that assumes you want to access Download mode to flash a repack firmware. Follow carefully; flashing can brick your device and will usually void warranty.
If Download Mode appears instead, your repack hasn't modified the bootloader keys. how to open fastboot mode on samsung galaxy a7 repack
Enable Developer Options, turn on USB Debugging, then run: Note: Samsung devices use "Download mode" (Odin mode)
She tried again, but this time, as the screen died, she swapped her thumb from Power to Volume Up . turn on USB Debugging
This is the most common way to access the hidden menu for Bootloader/Fastboot options: your device completely.