The official website for Dragon Ball Heroes has updated with a description for the first episode of the anime. Thanks to
kanzenshuu.com translator Todd Blakenship aka
@Herms98 , we have an English translation.
"Trunks returns from the future to train with Goku and Vegeta. However, he abruptly vanishes. The mystery man ‘Fu’ suddenly appears, telling them that Trunks has been locked up on the ‘Prison Planet’, a mysterious facility in an unknown location between universes.
The Group searches for the Dragon Balls to free Trunks, but an unending super battle awaits them! Will Goku and the others manage to rescue Trunks and escape from the Prison Planet?"
Fans are still wondering whether the promotional anime will receive an official broadcast on July 1. So far, the only announcement has been for a special screening in Japan's Aeon LakeTown in Koshigaya, Saitama Prefecture. It's also confirmed that the episdoe will be released online on the same date but most fans are hypothesizing that the anime might only air on the internet.
Stay tuned to Anime Mojo for word on whether Crunchyroll, Funimation or some other anime streaming platform announces that they've picked up the Dragon Ball Heroes anime.