USB method - Hard Reset a SAMSUNG (when the hard reset screen won't come up) 

If you are trying to hard reset a SAMSUNG, and you find you cannot bring up the hard reset menu, this is the answer. You might have watched other videos, but they forgot to tell you the most important part. YOU NEED TO HAVE THE PHONE PLUGGED INTO A PC using a data cable. There any many models where, if you don't have the phone plugged into a PC using the data cable, it won't bring up the hard reset menu.
As an example, IF your Samsung Hard reset screen is not coming up and won't work for you, this is how you actually hard reset your A21s.
HOW TO GET THE SPECIAL SCREEN UP: Plug a USBC cable into your PC / Computer. Hold down Power and Volume Down until the phone goes black / shuts down. THEN Hold the Power and Volume Up Buttons until the Samsung A21s screen comes up then let go. Wait 5 seconds and the hard reset screen will come up. The trick is, the phone must be plugged into a computer using the USBC Cable. Good luck.