Don't be.
I don't mind that.
I don't care [mind] a chip.
I'm not the least bit worried about it.
気にせずに
I'm not the least bit worried.
もう気にしない。
I don't care anymore.
I don't care a pin.
気にしないよ。
the act of taking no notice of something
He is a disagreeable fellow.
I don't care a rap.
Never mind about that.
I don't care a hill of beans.