Lay the aquarium on its side. The opening should be facing you with solid surfaces on the top, bottom, back, right and left.
Cut a piece of the sheet plastic that is one-half inch longer than the aquarium opening and 3 inches wider than the width of the aquarium opening. Attach the plastic to the top solid surface of the aquarium approximately 3 inches from the front edge with clear packing tape. Make sure that the plastic drapes over so that it completely covers the front aquarium opening and leaves no gaps.
Attach a clear thermometer to the back of the incubator with superglue. Check that the thermometer is straight up and down and the temperature is easy to read clearly. Place the small lamp into a far back corner of the incubator and run the cord out beneath the sheet plastic flap.
Screw a lightbulb into the lamp and plug the lamp in. Wait a few hours and check to see if the temperature is satisfactory. You may need to try bulbs of different wattages to find the correct one to achieve the temperature you require for the type of incubation you are performing.