I just googled "turn closet into incubator" and this guide came up. No idea how good of an incubator this makes though.
https://www.americanmadeexotics.com/...onversion.html
And if I were you, I would just DIY build another incubator using an old fridge or wine cooler off craigslist or something. It sure saves a lot of money and time either way, if that's your goal.
You need to install a fan.