The short lead end of the infrared is negative, while the long lead end is positive. Connect the negative electrode to the 5V interface as shown in the figure below, then connect the positive electrode to the 10K resistor, connect the other end of the resistor to the GND interface, and finally connect a jumper wire from the positive extreme column of the flame sensor, and connect the other end of the jumper wire to the simulation mouth as shown in pic above.