30-sai Mojo, Heisei Gyaru ni Naru.

Aya Tsurunaka, a 30-year-old woman who's never had a boyfriend, is just an ordinary office worker who regrets her life so far. She often wonders what her life would have been like if she had mustered the courage to become a "gyaru" (a type of fashionable, often heavily made-up girl) in high school—the very thing she secretly admired and loved. Then, good fortune strikes Aya. She's transported back in time to 200X and given the chance to relive her life as a "Heisei gyaru" high school girl!

(Source: Kadokawa, translated)