Hi there! First, You will need to move him off of that substrate. If you want, you could use cage carpet, but if you don’t have anything else paper towels will do. Aside from that, I would replace the light bulb with an led that doesn’t emit much heat (not enough to make any difference) and put that on a timer for 12 hours in/12 hours off. Then get a decent $20 thermostat and a heat mat. Leo’s are Nelly baskets, so heat from below is most helpful. Think about it— in the wild they’d be inside burrows during the day, and then at night they’d come out and lie flat against rocks that are still warm from the sun. Not giving them either belly heat or heat from a halogen bulb (which is much more expensive, since you’d need a dimming thermostat that will easily cost $150 or more) will easily cause eating issues.
As far as general care, I’d recommend looking at this care sheet. Unfortunately, a lot of pet store employees aren’t too knowledgeable about reptiles, and the care sheets that Petco/pet smart give you are equally uneducated.
https://herphusbandry.weebly.com/leopardgeckocare.html
nice gecko, btw!