Dokidoki! Precure: Mana Kekkon!!? Mirai ni Tsunagu Kibou no Dress

One day, Mana Aida receives a wedding dress from her mother and grandmother that they had worn in the past. While thinking about who she would wear this beside someday, a mysterious man named Marsh appears, and Mana is thrown back into the past. She was happy to see her grandmother she loved and her old dog Mallow, but she then realizes that Arisu and Rikka aren't there because memories have been altered. In order to save precious memories, the future, dreams and hope, Mana transforms into Cure Heart.

Synopsis from Anime News Network