If you are using mediteo without an account, press the profile icon in the top left corner which you can find on each page. Then press the edit icon in the top right corner of the profile page to change your profile data. If you are logged in with your CGM LIFE account, you can only change your profile data online e.g. at https://app.mediteo.com/en/login.
No, you do not have to enter any personal data into mediteo. You have the possibility to enter your name and date of birth on the Profile page, but this is voluntary and the data are only used to personalize mediteo.