Question:
BS"D
A goy that made neder for idolatry, now is doing everything to become a noach bnei, what should he do to nullify that neder?
What if a Jew who does teshuvah like he should also do to nullify that neder?
Answer:
A goy does not have the halachos and the mitzva to keep the neder that he made, therefore he doesn't have to do anything about it.
I don't understand your second question, the Jew is not the one who made that neder therefore there is nothing for him to do about it either.
Best wishes
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