I have a collection that needs to be updated. There's a need to add new field and fill it out based on the existing field.

Let's say I have a collection called `documents`:

```
documents/{documentId}: {
   existingField: ['foo', 'bar'],
   myNewField ['foo', 'bar']  
}

documents/{anotherDocumentId}: {
   existingField: ['baz'],
   myNewField ['baz']  
}
// ... and so on

```

I already tried to fire up local cloud function from emulator that loops for each document and writes to production data based on the logic I need. The problem is that function can only live up to max of 30 seconds. What I need would be some kind of console tool that I can run as admin (using service-account) to quickly manage my needs.

How do you handle such cases?