First enable OEM unlock in developer options. Than you install apk from first post, open it and apply for deep test mode. After few minutes when they approve hit 'Start deep testing" in this app, that will reboot device to bootloader. Then open folder where you have fastboot files, hold shift and click with right mouse button anywhere in that folder and hit "open command prompt here". Type "fastboot flashing unlock" and then on phone with volume buttons select "unlock bootloader". Now your phone will wipe device data and reboot. Now your bootloader is unlocked.