To do this, press the Option key on the Mac while it's on the blank white boot screen. If the Mac was powered off, you can choose which partition to boot before the Mac selects for you. In the Startup Disk, choose the 'Windows on BOOTCAMP' partition, and click 'Restart.' Then, confirm your choice to reboot to Windows. If you're in macOS, you can switch to the Windows partition using the Startup Disk utility within System Preferences.
