Redwood page customization - PO Line level Edit via Visual Builder

We are trying to redo existing Fusion field customization in Edit PO page to the new Redwood PO Page (Purchase Orders (New)) using Visual Builder. We were able to apply customization to PO Header (hiding a field), but from what I can see in Visual Builder, I cannot find an option to edit/customize PO Line/Schedule/Distribution.

For reference, we need to set quantity and line description to read-only in PO Line Edit (this exist in our current Fusion page setup). How to edit PO Line/Schedule/Distribution in Redwood page via Visual Builder?

I attached a screenshot of where I was able to edit/customize PO Header level.