We tie the bag and put on more bags, close them well. Leave overnight.
In the morning you will see that the grill is covered with pieces of carbon deposits and now, using a kitchen sponge, you can simply and easily clean it under running water.
Ammonia “works” not only when you soak something in it, but also when it evaporates. That’s why its vapors ate away all the carbon and grease on the grill.