While it may be tempting to present new arguments or evidence in your thesis or disseration conclusion, especially if you have a particularly striking argument you’d like to finish your analysis with, you shouldn’t. Theses and dissertations follow a more formal structure than this.
All your findings and arguments should be presented in the body of the text (more specifically in the discussion section and results section.) The conclusion is meant to summarize and reflect on the evidence and arguments you have already presented, not introduce new ones.