AFAIK, the exact streaming date has not yet been announced, but it is expected to begin streaming on Peacock by September or October, roughly three to four months after its theatrical debut:
From:
The Live-Action How to Train Your Dragon Movie Hits Digital One Month After Its Theatrical Release
By Jacob Kienlen, IGN - July 15, 2025
https://www.ign.com/articles/how-to-watch-how-to-train-your-dragon-streaming
When Will I Be Able to Stream It?
As a fan of the original How to Train Your Dragon movie, I don’t plan on paying any extra money to see what appears to be a 1:1 remake in live action. I will definitely watch it once it comes to streaming, however. Unfortunately, we don’t have any sort of official confirmation as to when it will actually come to streaming, but we do know that it’ll live on Peacock. Neither Universal Pictures nor the streaming service have made an announcement about the streaming release date.
That being said, Universal Pictures’ movies tend to come to Peacock three-four months after their initial theatrical release, though this depends on how well it continues to do in theaters. That would place estimations for a streaming release date somewhere in September or October.