Samsung Galaxy S6 (G920F)

                                                                                First switch off mobile phone.

   Press and hold mobile phone in Volume up(+) key + Menu key +Power Key in few seconds.

  Now you can see Android Logo on screen then press the  volume key to see recovery menu.

You select wipe data or factory reset or press center key to confirm.

You select yes or delete all user data and press center key. 

  After you reboot the mobile phone set end the process