Necromania: A Tale of Weird Love! (1971)

A couple having marital problems (the husband can't seem to rise to the occasion) visits Madame Heles, a necromancer, in hopes of ameliorating their boudoir blunders. After an elaborate ritual with a skull, Heles' lovely assistant Tanya first takes care of another client, then moves on to the couple, each in their turn. Once she's worked with each of them on a physical level, they are ready to meet the Madame, who will decide how best to help them.