The amendments you can make to an already filed EU trademark application are very limited. The EUIPO permits corrections to the applicant's name and address, and to errors of wording or copying, provided the correction does not substantially change the mark or broaden the scope of the application.
The representation of the mark itself cannot be altered in a way that changes its distinctive character. The list of goods and services can be limited (narrowed) but cannot be expanded after filing.
If a more substantial change is needed, such as adding goods and services or altering the mark, a new application must be filed.