There are three ways to factory reset HTEK 900 Series Phones.
# button
Press and hold the # button on the telephone keypad for 10 seconds and the press OK once the prompt shows up on the LCD
Menu Via LCD
LCD:Menu->Settings->Advanced(admin)->Settings->Reset, the screen will pop up on the lcd and you can select OK to factory reset.
Web GUI
Log into the phone's web menu via it's LAN IP address
Go to Management (top menu), Upgrade (left menu), Reset to Factory (middle of page).