How to force a factory reset or hard reset on Symphony devices

Symphony P7 Symphony P7
Symphony i50 Symphony i50
Symphony ZVIII Symphony ZVIII
Symphony P7 Pro Symphony P7 Pro
Symphony V47 Symphony V47
Symphony V120 Symphony V120
Symphony i21 Symphony i21
Symphony P9 Symphony P9
Symphony Z9 Symphony Z9
Symphony G20 Symphony G20
Symphony i10 (2GB) Symphony i10 (2GB)
Symphony i20 (2GB) Symphony i20 (2GB)
Symphony i10+ Symphony i10+
Symphony P8 Pro Symphony P8 Pro
Symphony Z10 Symphony Z10
Symphony Roar V95 Symphony Roar V95
Symphony i90 Symphony i90
Symphony V75m Symphony V75m
Symphony INova Symphony INova
Symphony V75m (2GB) Symphony V75m (2GB)