Add the rice vinegar, sugar, water, and sambal oelek to a small sauce pot. Heat and stir the mixture over medium heat until the sugar fully dissolves.
Stir the cornstarch into 1 Tbsp water until dissolved, then pour it into the sauce pot with the sweet chili sauce. Continue stirring and heating until the mixture comes up to a simmer, at which time the cornstarch will thicken the sauce and go from appearing cloudy to clear.
Use the sauce immediately, or refrigerate and use within one week.
Easy Sweet Chili Sauce https://www.budgetbytes.com/easy-sweet-chili-sauce/