To be clear, this is new content and not the two-part compilation films that are releasing soon. No premiere date announced yet. Check out the ANN article for additional information. Synopsis for the first season from AniList:

Feeling out of place in the countryside, high school dropout Nina Iseri moves to Tokyo. After a rough first day and getting locked out of her apartment, she meets her favorite guitarist, Momoka Kawaragi. The two put on a street performance together and decide to start a band with three other girls. While each girl faces her own struggles, their passion for music keeps their dreams alive.