You might need to take these to the dry cleaners that does alterations and repairs for a steam pressing. That might be the safest option of the pieces were expensive. Explain what happened and ask if they would be able to help. Some places can do wonders when repairing laundry errors.
Alternately, you can try a professional technique at home: Damp pressing. This can be used on the skirt, but not the sweater. Use your regular iron and a spritzer of water. Spray on some water and then press until steam rises. For setting pleats and taking out wrinkles in my workshop I use something called "The Rajah Press Cloth" I learrned about this when I did alterations and repairs. It is available at many sewing and fabric stores. It has chemicals in it that help press out creases and press in sharp pleats and creases. You spray the cloth with water, place it on the garment and then press until the cloth is mostly dry. The creases will be gone and the pleats will be re-set. Be sure to use the correct iron setting: wool works best, it's less likey to scorch than cotton or linen. More heat doesn't always give a better result.
For the sweater you need to steam block it. Knitting websites have more detailed explanations of blocking knitted sweaters, but I can describe some of the basics. In blocking you use heat and steam to coax the sweater inot the desired size and shape. When knitted items come off the needle they are often stretched and distorted and they need to be blocked into shape. The following method is for sweaters that are very distorted. You pin the sweater onto some type of surface in the size and shape you want. You place a damp cloth over the sweater and spray on more water. You then use the iron set to the highest steam setting and medium heat setting and steam through the damp cloth and into the sweater. Don't press the sweater, merely hover the iron over it. After steaming it allow it to dry flat. It should be back in shape and it should be less wrinkled. If the sweater is wool be sure you don't shrink it too much, if it is synthetic use a lower iron temperature because some synthetics melt under high heat.
After re-blocking the sweater will be a bit more fragile. From now on wash on delicate and air dry. Any further machine drying will bring all the wrinkles back.
I did alterations and repairs for many years and that's how I would approached the repair of those peices