Hard Reset SAMSUNG J210F Galaxy J2 (2016)
1) The device must be switched off, so hold down the Power key for a few seconds.
2) Afterwards press and hold together: Volume Up + Home + Power button for a couple of seconds
3) You can release held keys when the Samsung Logo appears on the screen.
4) Then select from Recovery Mode menu "wipe data / factory reset" using Volume buttons to navigate and Power button to confirm.
5) In the next step choose "Yes -- delete all user data" to confirm the whole operation.
6) When the Recovery Mode appears again on the screen select option
"reboot system now".