Our service, Birthday Calendar by Davia, doesn't have the function of editing birthdays.
However, our similar service, Birthday & Greeting Cards by Davia, has that function.

On Birthday & Greeting Cards by Davia, you can add, update and delete your friends’ birthdays.
To find this function; click below the URL to visit our website, click Birthday Calendar, and then, click "Manage Birthdays".

Birthday & Greeting Cards by Davia
https://www.holidaycardsapp.com