How do I change the temperature sensor under the

It’s located on the driver’s side of the engine on top /side of the head.. midway.. I don’t think you need to remove the engine cover to see it.. if it is the correct one it will have a dark green top.. the bad version has a black top… but they can all go out to lunch on you if old enough.

To replace.. make sure the car is cool..
You need a hood tool.. or small pair of pliers to remove the retaining clip that holds it in place.
Place a rag under and around it to catch the coolant.. you will lose less than a half a cup.. if that.

Pull the retaining clip back toward you.. try not to drop it.. (another good reason for the rag)

Wiggle the sensor.. pop it out.. and replace with the new green top one make sure you clean the area well.. and when you reinstall the new one that the c clip goes back on straight or it will leak.

Once you see the part out of the box.. you will understand how it works

Start the car.. check for leaks.. run until warm with the heater on.. top up the coolant overflow bottle with distilled water.. (if more than a half a cup.. you should mix the proper anti freeze and distilled water and then top up with that)

Good luck