Make the sauce and marinade. Combine the soy sauce, minced garlic, brown sugar, olive oil, and red pepper flakes in a measuring cup. Then, pour half in a saucepan and keep the other half for the marinade.
Thicken the sauce. Add 3/4 cup of room-temperature water to the saucepan. Take out a few tablespoons of liquid to be mixed with cornstarch, then add it back in. Bring the sauce to a boil, then simmer for 5-8 minutes until it has thickened.
Cut and marinate the steak. Cut about 1 1/2 lbs. of steak into pieces that are 1-2 inches thick. Place them in a ziplock bag with the marinade and then let them sit for at least 3 hours, or overnight.
Cook. Place the steak bites in the air fryer basket and cook for 8 minutes at 400 degrees Fahrenheit.
1. Serve. Drizzle with sauce and then serve with your favorite sides.