If your swimming costume straps are too long, the suit will not provide proper support and the straps may slip down when you move. Unattractive horizontal wrinkles in the front of the top of the suit are a sign that the straps may be too long. If a young girl's tank-style swimming costume sags in the seat, you can improve the fit by shortening the suit's shoulder straps.
Remove the seams at the shoulder with a seam ripper.
Try on the suit. Pin the straps in place so the suit fits smoothly and provides the support you desire. Sit down in the suit to be sure the shorter straps are not too tight.
Pin the straps together at the desired location. The right sides of the straps should fit together.
Sew one of the straps together with a straight seam. Fold out the seam allowances and sew on the outside of the suit 1/4 inch from the seam on each side of the seam to hold the seam allowances flat. Sew the other strap in the same way.
Cut the excess fabric off the straps 1/2 inch from the seams. Finish the cut edges with a zigzag stitch.
Remove the seams that attach the straps to the body of the suit in the back, using a seam ripper.
Pin the strap to the suit so the right side of the strap is against the inside of the suit.
Try on the suit and pin the straps in place. The suit should fit smoothly and provide support. Sit down in the suit to be sure it is not too tight. Adjust the length of the straps until you are pleased with the fit.
Sew the straps to the top of the swimsuit. Sew a straight seam using a sewing machine and thread that matches the suit along the top edge on the outside of the suit and through the straps. Sew another seam 1/4 inch below the first seam.
Cut the excess fabric off the straps 1/2 inch below the second seam and finish the cut edges with a zigzag stitch.
Do not twist the straps when you sew the straps in place.