The system says four units are in that location and there is one on the shelf. What do you do, and how do you stop it happening again?
Block the location first so nothing allocates against a figure you have just disproved, then correct it as a recorded adjustment with a reason rather than an edit. Accuracy is maintained continuously by cycle counting, because stock records drift even in a well-run warehouse. It also connects inventory accuracy to the point an interviewer is testing.