“Nah” has two meanings in the Brunei Malay language.
The first way you can use it is similar to how you tell someone “I told you so” / “That’s what you get” / “Look what happened.” It is said when the person has already been warned, still does it, and the outcome is what was expected.
An example is, “Nah.. Baru jua tagur” which means “See what happened? We just mentioned about it.”
The second way you can use it is if you pass an item to someone and you want them to take it from you quickly.
An example is, “Nah, ambil tah” which means “Here, take it.”