1·I need to lengthen this skirt.
我需要把裙子放长。
—— 《牛津词典》
2·The skirt hemline should be at or below your knee to slim and lengthen your look.
裙子的底边及膝以下可以拉长身材。
3·Ask the tailor to lengthen this skirt.
请裁缝把这条裙子放长。