If your custard smells bad after making it then it's likely been overcooked.
You can make your custard smell better and fix the overcooked custard easily.
To fix overcooked or burnt custard all you have to do is add custard powder, sugar, and water to a bowl and mix them well.
Later, add the mixture to the boiled milk.
Whisk all of it properly so that the custard is super delicious.
The smell of custard will overcome the smell of burnt milk.