^^^ That is really a more distant option honestly, as it resets all WiFi network access as well (and hopefully the person that does it has the passwords they need to sign into said networks when they attempt to do so after the reset).
The best option is to go into your network settings and make sure your cellular data is on and that the personal hotspot option can be accessed from that menu, many times turning it on in there will make the option reappear in the main menu area. If you're still having problems afterwards, a simple hard restart of the phone is a good remedy...hold the home and power button for 5-10sec and allow the phone to restart, your personal hotspot option should have returned.
If neither of those fixes does the trick, a network reset may be necessary.