Flipping an omelette can be tricky, but with practice, it becomes easier. Once the edges of the omelette are set and the center is still slightly runny, use a spatula to fold one side of the omelette over the fillings. Then, tilt the pan slightly and use the spatula to gently fold the other side over. If flipping the entire omelette feels challenging, you can also finish cooking the top by placing the pan under a broiler until it's set.