I cannot find any sources that indicate any sizeable or even notable examples of German conversions to Judaism during the Third Reich period. Pre-war data shows that most conversions were due to a Gentile marrying a Jew, especially Gentile women marrying Jewish men. Of course, once Gentile-Jewish marriages and relationships were outlawed and discriminatory laws against racial and religious Jews were passed this cause of conversion would have become non-existent and many converts actually reverted for the sake of preservation. Conversion to Judaism during the Nazi era in any public capacity would have been a near-suicidal act, and I think it’s fair to claim in the absence of evidence that such conversions were unheard of.

Source for Gentile conversions and mixed marriages: https://www.jstor.org/stable/4464869