Firebase - adding a new column to all the existing rows

Ionic Framework ionic-v3
1

Old DB:
I have a old firebase realtime database. Which have timestamp with all data. My ionic 1 app can display descending with it.

  "birds" : {
    "userid" : {
      "one" : {
        "name" : "Robloks to dobra gra",
        "created" : 1523338713421,
      }
    },

New DB
I rebuilt the app with ionic 3.
where I added a new column “created_descending”, filled with negative timestamp value for descending purpose.

  "birds" : {
    "userid" : {
      "one" : {
        "name" : "Robloks to dobra gra",
        "created" : 1523338713421,
      **"created_descending": -1459361875666**
      }
    },

Now, I need to update all the old rows/nodes, to insert this new column “created_descending”.

My Question:
So, What is the easiest way to add this column (negative values) to each existing rows?

Note: Sorry, I used the term “table, column, row” to explain my need. I know they are not appropriate for firebase.