Welcome
@PinkyLepuce
I'm sorry your plumeria broke and I am mystified why it is so hollowed out! Has it been very dry where you live?
This is what I would do.
I would replant the bottom section as is and it will eventually make new branches from the old leaf scars on the broken section.
The piece that was broken off, I would first remove (clip) all the leaves; then I would cut just above the V into two cuttings, dip them in a rooting hormone or similar, let callus for a week and then plant them in a perlite or sand-heavy mix and they will most likely root.
Look at it this way: if all goes well you will eventually have three plants!
