Don't trouble about it; don't worry about it; don't be concerned about it; forget it; skip it. Usually used in speaking or when writing dialogue.
"What about money?" "Never mind that. I'll take care of it."
"What did you say?" "Oh, never mind."
Never mind preparing a picnic lunch; we'll find a lunchstand when we get to the beach.
So you weren't listening to me again. Never mind; it wasn't important.
When he spilled his drink on my coat, I said, "Never mind. It needs to be cleaned anyway."