I can´t find a real answer to this on the internet. It seems like Hitler used the death of Hindenburg to get into both positions, but how? Was it another 'Notverordnung'?
Hitler merged the two position. When Hindenburg died, Hitler chose not to have new elections but instead held a popular vote of the merging of the two offices. Hitler's government passed a law merging the two offices on August 2, 1934 and on August 19, 1934 a popular vote was held intended to gain popular approval for this measure. As expected, about 89% of all votes voted yes in what can only be described as a rigged vote.
Sources:
Peter Hubert: Uniformierter Reichstag. Die Geschichte der Pseudo-Volksvertretung 1933–1945. Düsseldorf 1992.
Otmar Jung: Plebiszit und Diktatur: die Volksabstimmungen der Nationalsozialisten. Die Fälle „Austritt aus dem Völkerbund“ (1933), „Staatsoberhaupt“ (1934) und „Anschluß Österreichs“ (1938) (= Beiträge zur Rechtsgeschichte des 20. Jahrhunderts; Bd. 13). Mohr, Tübingen 1995.
Ian Kershaw: Hitler.
Verordnung zur Durchführung der Volksabstimmung über das Staatsoberhaupt des Deutschen Reichs.