What does it mean:
Halt das Schicksal auf, gib mir was einst war mein.
This seems to be from a poem or the like, probably from a fairy tale. It is hard to understand if you don't know the context. It's easy to translate, though: "Halt das Schicksal auf" translates literally to "stop fate". "Gib mir was einst war mein" means "Give me what I once owned". It's difficult to relate these two half sentences without knowing what is referred to with "what I once owned" or what kind of fate is to be expected.
After watching this (provided by the author of the question in a comment) I'm rather sure that "give me what once was mine" refers to youth ("give me my youth back"), and then also "stop fate" makes sense (getting old being fate).
The original incantation is:
The German translation of this song is:
The idea behind is that the healing incantation kept the old witch young, so to say stopping the inevitable process of aging ("the Destiny").
P.S.: After having written the answer I have noticed that the author of the question already provided the link to the original, so my suggestion was correct.