see: Enum.find_index/2
EDIT: OP did not post a map.
Note, that your map-items will be passed as {key, value} to the function.
See the example at the beginning of the Enum documentation:
map = %{"a" => 1, "b" => 2}
Enum.map(map, fn {k, v} -> {k, v * 2} end)
[{"a", 2}, {"b", 4}]
