how do i fix the engine temperature gauge its not working at all?

Sounds like if you have multiple gauges experiencing a problem that you could have some kind of trouble with the instrumentation itself, or the wiring to it. Testing will have to be performed first hand to see what is going on. A good diagnostic tool is able to monitor body components, including commanding the gauges in question to see if there is a problem with the wiring or affected gauges themselves, and can also test the "inputs" to those gauges to check for data incoming.