HardReset.info:
1- In the first step you need to hold down Volume Down and Power keys for a few seconds.
2- If the screen goes dark start pressing Volume Up + Power button.
3- When the SAMSUNG Galaxy M21 logo appears let go of all keys. The Recovery mode on the screen.
4- Now use Volume buttons to choose Wipe data/factory reset. Use Volume buttons to scroll down and the Power key to accept it.
5- Then select Factory data reset by using the same keys as before.
6- At the end choose Reboot system now by using the Power button.
7- Well done! All your data was removed during the whole operation.
