Pokemon Scarlet And Violet The Teal Mask will be released at the same time across the world on September, 12
To start a DLC you will have to go into Nintendo Switch and update the Pokemon Scarlet And Violet game after purchasing the DLC
Before buying the DLC, cross-check at once that all the information the account provided by you is correct. You can access the expansion only through the account
To get into the region of Kitakami, you have to first reach the Treasure Hunt main story arc which shouldn't take long.
After completing the treasure hunt at Kitakami you will receive a Rotom call from Professor Jacq where he will invite you to travel the land of Kitakami
Keep in mind that, The Teal Mask DLC that becomes available on September 12 and 13, 2023. The Indigo Disc will be released in the Winter season.