This works best on fat quarters and easily managed cuts of fabric. Lay out a towel on a table or other flat surface that can get wet. Put fabric in water as hot as you and it can stand without shrinking. Don't wring the fabric or do anything to make more wrinkles, just swish it around and get it good and wet and warm. Put the fabric on the towel and smooth out as much as possible to let dry. Can stack a few pieces but don't get carried away.
Not the best method in the work but it helps flatten out fat quarters that have been rolled or folded.