I think you might even need to go more fundamental than just telling them what do to.
They may not have the foundational understanding of what money is and how they exchange their work for value. Once they understand it, they will be less likely to be antagonistic during price drops.
The guy wrote an article about his approach and how he did it. I haven't read it myself but perhaps you can get some good info out of it.
https://jamessharman.substack.com/p/the-staff-shortage-restaurants-and