-Let the person figure it out.
-Discipline the person involved.
-Wait for an opportunity to help the person see the error.
-Stop the person and show him or her how to do it correctly.
Job hijacking happens more than you think. When the boss stops an employee in the process of doing a task, takes it over or sends them to do something else, you have just witnessed a job hijack in progress. It is frustrating for the poor employee because they have been robbed of the opportunity to learn something and the satisfaction of figuring something out and doing their job.
Discipline is not always the best approach to making sure things get done correctly. Because eventually an employee who is constantly being corrected gets tired of getting corrected all the time. Without a change they will likely quit and move on to another job.
The most productive and enlightened strategy is to wait for the right time to help the person involved toes the error of their ways; then they will naturally take corrective action.
Simply letting someone figure it out is a passive approach to management, and unless the person has their own high standards and a strong work ethic, you cannot expect much. People naturally rise to a challenge and managing passively is not a challenge for you or the employee. Raise the bar!