"Firm command" means having complete control and authority over a situation or someone, and ensuring that they follow your instructions or obey your orders without question. Full definition
If you see your child attempting to climb out of the crib you certainly can try to discourage him with firm commands that this is not allowed. (verywellfamily.com)
Most dogs respond well to rewards and praise, while a few breeds need firm commands and rigorous discipline. (web-rover.com)
Achieved firm command of but not limited to: Aircraft inspection criteria, safety of flight issues, hanger and flight - line aircraft system operational checks. (jobhero.com)