This gesture should only be used if you have a good rapport with your students and they feel comfortable in your learning environment.
The reason for the caveat is that it could make your learner self-conscious. It should be balanced with equal amounts of positive reinforcement such as “Good effort!” or “Keep going!”
To achieve it, rock your head from side to side and scrunch up your features. This will encourage the learner to self-correct.
Remember that you should praise their effort, whether they can find the correct answer or not.