Help! How to remove wrinkles from polyester dress!!!

Ask a qualified seamstress/costume mistress! They deal with all sorts of fabrics and have tricks of the trade to help with these issues.

I hang most things with wrinkles in the bathroom and keep the door closed when I shower and that usually helps a lot. If that doesn't take them out, I'd probably try a handheld steamer on a low setting (try testing it somewhere that won't show too much). It's surprising to me that Lulu's discourages steaming for polyester. I'd be careful not to expose it to high temperatures (like with an iron, high-heat close steaming, or a hot dryer), but I've never heard of polyester not being gently steamed. What are the washing/cleaning instructions? If it can't be dry cleaned, then I'd expect it to be washable? If it is, then I might mist it and then put it in the dryer on a no-heat "fluff" setting, with a clean white towel or two and let it tumble, but check it every couple minutes. Good luck!