The official trailer for Doctor Who: The Power of the Doctor will be tomorrow (Saturday October 8).
This episode releases sometime during October and will see the return of two former classic Doctor Who companions, alongside the Thirteenth Doctor, including Sophie Aldred (Ace) and Janet Fielding (Tegan Jovanka).

Doctor Who: The Power of the Doctor | Teaser
BBC have also teased a new clip from the trailer.
Jodie Whittaker’s final episode will see her regenerate into the next actor. There’s been a quite a mystery if this will be David Tennant again and then Ncuti Gatwa after. It’s not yet clear, however David Tennant, Catherine Tate, Bernard Cribbins and more of the Noble family will be returning for a 3 episode special. There are also some of the aliens revealed for the 60th anniversairy.
Unless the BBC is making an update to the TV guide, it looks like the Doctor Who: The Power of the Doctor episode will be premiering between October 14 – 31. Previous episodes released on Sundays, so could be on October 16, 23 or 30.