How to populate a table programatically

[rodbs]

I want to populate the first header row of each table programatically
I've managed to get the first cell doing that:

   const firstDescendant = tableNode.getFirstDescendant()
     if ($isTextNode(firstDescendant)) {
          firstDescendant.select()
          firstDescendant.setTextContent('Hello')
      }

But how to select next cells?
When using this method getDescendantByIndex() I don't see a pattern in the index values...