Bayern munich has been inconsistent in the bundesliga this season, they are still close to the top of the table and if they beat Hertha Berlin today they will take the first position from Dortmund. The bundesliga is not so competitive, because even if Bayern munich do not play well they can still win the bundesliga title, and if they win it this season, Dortmund should know that they have let their fans down because this season was a good opportunity for them to win the title from Bayern munich after many years of them winning it.
It seems to me that Dortmund itself does not believe that they can win the Bundesliga, everyone is so used to the dominance of Bayern that it is difficult to think of another outcome, even when Bayern is not in the best shape. Tuchel, of course, will try to win this match and the Bundesliga, although I am sure that he was not invited to the team for this, the original goal was to win the Champions League.