In this case, it means communicating to the head chef that there is no chicken and suggesting a change to the menu. If the boss accepts, the task has been changed: now what is expected is not rice with chicken, but... rice with pork or soup or something else, and if everything is done right, that is what you will get. Now nobody got it wrong. To change the task definition is to go back to the outline suggested on page 13 and make changes to fit reality.
If the boss still does not accept, you will have to buy the chicken or buy the rice already prepared, whatever, but without the necessary resources - no matter how lucky you are - you will not get the expected products (results).