How to update denormalized documents

I found same articles saying we need to index denormalized documents if we want to use joined tables in App search.

However, I have not found any article referring to how to update the denormalized documents as far as I've googled.
If you guys know some best practice, could you share it?

To my knowledge, we do not have a guide like that.

Could you give us an idea of what your denormalized documents look like and what specific issues you're having when updating?