replies: Array
>0: Object
   _id: ObjectID('6295cefdfab3e2399813bb0c') 
   userID: ObjectID('624eb07040613618bc358d0d')
   reply: "hie"

Now i have to populate userID from an array showing its firstName and email and my code is this which isn't working

.populate("replies.userID", "firstName email ")
    .populate("userID", "firstName email")
    .exec((err, result) => {
      if(err)
      console.log('nothing is shown',err)
    })