The fibers need to be uncompressed. The fold in purchased fabric are mechanically folded with high heat and pressure. The fold compresses the natural fiber. One way is to soak the fabic in water , the longer its been folded the longer it should soak. Iron silightly moist. It is always a concern when buying true vintage ... the fold may never be completely removed.
Think about it like paper (made from natural fibers) can you ever really get a fold out? If you rehydrate the fiber and press you can . FYI some fibers if folded do get a permanent crease.
Remember to refold your quilts ever few months.