The first episode of Grand Blue Dreaming Season 3, titled "やり残し" (Unfinished Business), began airing on July 6.
The episode aired at 24:00 on TOKYO MX and BS11 on Monday, July 6, followed by MBS on Tuesday, July 7 at 26:30, and AT-X on Thursday, July 9 at 21:00.
Streaming details are available on the official anime website.
Announced 7/6. Source: Official X (@gb_anime)