[Yodaman]

Well for starters, that house wrap or Tyvek is a essential part of the equation. It should have been done prior to installing the new construction windows, and it would saved the sheathing under the window.
I suggest watching several videos on how to properly flash a window. Too difficult to explain in a post.

https://www.finehomebuilding.com/2008/07/03/installing-and-flashing-windows-correctly