There isn't a ton of information on How To Train Your Dragon 3, but we do know, confirmed by Dean Deblois, the film is going to pick up where the books left off, which is about why dragons no longer exist. We also know that Drago, the villain from the second film, is going to return.
Release Date: March 1, 2019
Director: Dean Deblois
Writer: Dean Deblois
Composer: John Powell
IMDB Page: http://www.imdb.com/title/tt2386490/