What are you trying to achieve in the first place?

I made a wrong installation and I want to start from the beginning.

Windows key +R Type%appdata% and press enter. delete the thunderbird folder that appears. Restart Thunderbird.

Note that all mail and calendars will be deleted by doing this. It is rare that a start over really fixes anything. but doing this will give you that. There is no need to reinstall.

Thank you very much. Problem ist solved! Great!