As Pugs1975 pointed out, you can use the gear icon in the upper right of your notifications and quick set settings to access the main settings page, or simply say, "OK Google, open phone settings". I have to ask if you bought the device online, if so was there any mention of rooting the device in the description? The only way you could have possibly lost this functionality would be thru a bad root job. When you factory reset the device did you use the physical keys or the reset in the menu? It would be well worth you time to boot the phone into the bootloader menu with the physical buttons. This is usually accomplished by holding the vol button up or down while restarting the device. I believe there's a device that requires you to hold both during this process, but a quick Google should give you the step by step you need. Once in the bootloader at the top it should give you a status. The status will say, locked, unlocked, and or tampered. If you have either of the latter the device has been unlocked art some point and probably rooted. If you find this to be the case take your question over to XDA Developers and see if they can help you. There you find more on rooting and people who are more familiar with the ins and outs of adding things back.