I use pepper extract like this:

https://www.amazon.com/Million-Scoville-Pepper-Extract-Sauce/dp/B00DO6YZ8K?th=1

You have to be very careful. Like dip a toothpick in the extract and then stir it in your food. You will not taste a thing, but the heat will be there. If it's no hot enough move up to dipping a chopstick.