The display shows 'cool'

COOL on the display means that the oven thinks the oven is still to warm (usually after a self cleaning cycle). This is either a bad oven sensor or a bad display relay control board. You can’t test the board but you can test the sensor. Open the door and remove the 3-4″ long thin metal rod attached to the back wall. There are 2 screws holding the sensor on that you can remove and then pull the sensor forward until you can disconnect it. With a multimeter, check the resistance of the sensor at room temperature and it should be about 1080 ohms. If it’s not, replace the sensor, otherwise you need to replace your relay board.