Here is a guide on How To Hard Reset RM-1099 MICROSOFT Lumia 535. The phone must be off.
1. Press and hold both Volume Down button and Power On Button. You will see an exclaimation point, release both keys or buttons.
2. Press the following sequence, Volume Up Button>Volume Down Button>Power Button>Volume Down Button. The phone will reboot. Then you willl see a gear-like icon as shown in the picture below.
3. Wait until finish. After that, the phone has been back to factory default.
