Your username and email address associated with your account can be changed only on the musescore.com website, not in the mobile app.
Here is a short instruction on how to change your login details:
- Log into your account on the musescore.com website
- Go to the Account Settings or click your profile icon located at the upper right of the MuseScore website and choose 'Settings' in the dropdown.
- Click the Account tab and update the information.
Don’t forget to save changes!