Ahsoka directs Din Djarin to Tython after meeting Grogu. She points him toward the ruins of an ancient Jedi temple, where Grogu may be able to contact another Jedi through the Force.
The direction comes after the events on Corvus. Ahsoka communicates with the Child and learns that his name is Grogu, that he was raised at the Jedi Temple on Coruscant, and that he survived the fall of the Jedi Order. She refuses to train him herself because she senses fear, attachment, and the danger that he could follow a dark path.
Tython is not the same place as Coruscant, Mandalore, or Nevarro. Coruscant is connected to Grogu’s early Jedi life; Nevarro is one of Din’s recurring stops; and Mandalore is central to Din’s later story. On Tython, Grogu’s Force call ultimately draws Luke Skywalker, who takes him for Jedi training.