fret not
Don't worry! Fret not—it's really not a big deal. Fret not, I'll take care of it.
Fret not!
Inf. Don't worry!; Do not fret about it! Mary: Oh, look at the clock! I'm going to be late for my appointment! Bob: Fret not! I'll drive you. "Fret not!" said Sally. "We're almost there!"