How to populate denormalized NoSQL views

Question

I have a todo app built with Firestore NoSQL db.

The data in the database is query-oriented denormalized data.

I wonder what the best way to populate new views in the db after there is already prod data for some of the other queries.

Example:

In the todo app, the data structure is like this initially:

• userid
  • plan
    • todo items

Now I want to create another page called inbox, for todo items that are not planned

The structure is now:

• userid
  • plan
    • todo items
  • inbox
    • todo items

This would require me to populate the inbox with todo items that are not queried.

Or any feedback on how this might be done in a better way?