How do I edit the topic in the Topic List that my student is enroled for?

Click on the "listed in Lists of Students" link for the respective student to display the topic, which you can then edit using "View operations" → "Edit". Don't forget to save your changes. If you are editing a topic after you have transferred the data from the Topic Lists to the Final Theses (procedures vary between faculties), inform the relevant persons (typically the study department, the department’s assisstant) about the changes.