1. Open the Starbucks app in your phone.
2. Go to the "My" page of Starbucks app and click "Avatar" in the upper left corner.
3. After opening the personal information page, click "Birthday".
4. In the pop-up window, select a new birthday date, and then click "Save".
After completing the above steps, your Starbucks birthday information has changed. If necessary, you can also consult Starbucks official customer service.