Wow, this is a little difficult to differentiate them, but if your eye prescriptions are the same or the contacts are zero diopter, it is not a problem, because why we make them right or left is to make sure that both prescriptions are fit for our eyes. If there's a big difference between your eye prescriptions, you can try to tell it one by one. For example, wear one of them in your eye, if it is comfortable, that's the right one, if it is not comfortable, put it in the other eye, and try to find which the best is. If you still can not tell them in this way, I suggest you turn to the optical shops where you bought them, and ask them for help.