No. Agonal breathing is a brain stem reflex, not real breathing. The person is unresponsive, the heart is not circulating blood, and oxygen is not reaching the body. Without immediate CPR and defibrillation, they will die.
This is one of the most dangerous misunderstandings in bystander response to cardiac arrest. Because the chest still moves and there is still some sound of breathing, witnesses often assume the person is breathing normally. They wait for paramedics instead of starting CPR. By the time help arrives, the chance of survival has often gone.
If someone is unresponsive and you see agonal breathing, treat it as cardiac arrest. Call 999 and start chest compressions. You cannot make things worse, but you can save a life.