I was baffled by the genitive singular "muneris".
Context: An amazing transformation occurs: Iolaus, a grown man long before, appears, miraculously restored to first young manhood. Asterisks mark the problematic words.
hoc* illi dederat Iunonia muneris* Hebe
victa viri precibus.
Iuno's daughter Hebe, won over by the pleading of the man , had performed this of service for him
Here is my construction of "hoc . . . muneris": ...