This is a movie I saw between the years 1965-68, black and white, about an expedition team in the jungle that find some kind of ring that had two(?) dagger prongs on it that you had to stab into your victim. Their blood would mix with the potion and from there on somehow you could become young again.
There was a scene where a man died sinking in quicksand, but not before they stabbed him with the ring.
At the end of the movie a woman from the expedition team is coming down some stairs and somebody finds her out, she goes back up the stairs and screams falling out a window and crashing onto a car in the street below. It shows a closeup of her face and she is old. End of movie.