Tomorrow I'll Wake Up and Scald Myself with Tea (1977)

Former Nazi Klaus Abard survives to the 1990s by taking anti-ageing pills. He plans to use a time travel trip to return to Germany in 1944 and present Hitler with a hydrogen bomb, so that he can win the war. Unfortunately the pilot, woman-chasing Karel Bures, dies on the morning of the trip and his earnest twin brother Jan impersonates him, without knowing about the plot.