To change your birth info in the app, just go to the top right menu > account settings > EDIT and you can change your birthdate, time and location here.
If you're not able to change your birthdate in the app because it keeps defaulting to today:
If you cannot update your app or iOS, you can choose your year first, it will unlock the month and date. It's a weird 2021 issue where, because you can't pick a future date on the app, if the year is set at 2021, it won't let you pick a future month.
If you continue to experience birth info issues, please contact us with your CHANI account email, birth info, screenshot, type of device and operating system.