When device is off, press (also hold) volume down key and then press (also hold) power key. After the device vibrates, release power key (keep holding volume down key) to enter recovery mode.Select "wipe data/factory reset" by volume down key (or volume up key), and then press power key.Select "Yes -- delete all user data" by volume down key (or volume up key), and then press power key to start reset.After reset is completed, select "reboot system now" and press power key to reboot your device.
Heating issue is common is all the smartphones nowadays, the Zenfone 3 Deluxe is not an exception to it. When played games or while using internet for too long without any pause,but after I kept it on standby for a little while, it cooled down real soon.
At this price point or even at lower price there are phones available which offers almost similar specification so until you are so impressed with the look and feel of the device I would not recommend buying this phone.