You can iterate a map with Enum.map for example but note that maps are not ordered so it is not guaranteed that you get any specific order for the users.

Example:

iex(1)> Enum.map(%{"a" => 1, "b" => 2}, fn {k, v} -> {k, v + 1} end) |> Enum.into(%{})
%{"a" => 2, "b" => 3}

Unsure where you want the initiator value, in the metas list or somewhere else? What do you want a single user map to look like?

This kind of sounds like an XY problem (I don’t understand why you need to do this), but here’s something:

updated = for {{user, val}, i} <- Enum.with_index(your_data) do
  meta =
    hd(val.metas)
    |> put_in([:initiator], i + 1)

  updated_val = put_in(val[:metas], meta)
  {user, updated_val}
end

updated_map = Enum.into(updated, %{})