This is a long thin tube like part located usually in the top rear of the oven. It is held in by 2 screws. This can easily be removed by removing the 2 screws and carefully pulling it out. Usually there will be wires connected and insulation so you will need to work it out. Then unplug the connector and check with an ohmeter. It Should have around 1000-1100 ohms if not replace the sensor.
If your oven has a Knob it has one of several styles of adjustments that can be made to it. First remove the knob it should pull right off. Now look on the back, if it has a little plate with a couple screws this is how you can raise or lower the temperature. There should be a little arrow or + - indicating to raise or lower temperature. This is how to adjust this type. Next is a small screw it is usually takes a very small flat head screwdriver. It is located in several different places including down the center of the shaft the knob is attached to is the screw. It is way in there you will need a flashlight to see this. Turn this screw in small increments 1/4 turns clockwise to lower temperature and counterclockwise to raise the temperature. Now if the screw is not down inside the shaft look around the shaft it is usually a brass screw it could be anywhere around the stem this screw should be adjusted the same as the other. The next type is an electronic type and these can also be adjusted by entering a service mode. This procedure differs among the many models you will need to refer to the owners manual for this procedure. Check the temperature sensor in electronic units first since that would be the most likely problem unless it is a brand new installation. In the case of new installations the control may be in a celcius vs farenheight and most have about 25 degrees of adjustment.