Once you have transferred the prefill data to your tax return, you can unfortunately no longer adjust it.
However, you can check the data before you finally retrieve it. If they are not correct, you can decide not to use certain prefill data and instead enter your information by hand in your tax return.
You can easily check the retrieved data:
Open the tax year you want to work on and click on "View prefill data". Now you can view the data in advance and check whether it is correct.
If you have noticed errors, you can refuse to transfer certain data. Simply start processing your tax return. For each question in the app that includes a data retrieval, you can now decide separately whether you want to use the prefill data or type in your data yourself.
In case your last name has changed, we would ask you not to transfer your personal data and to enter it by hand. In future years, the data will be updated.
If you notice differences in the income tax data, it is possible that your annual payslip (Lohnsteuerbescheinigung) is not up to date. You can ask your employer for the latest version.