You don’t. A DVD-R is not writable. Use a DVD-RW or whatever is appropriate for whatever DVD burner that you have. — Tom
In more detail, you don’t “make” a DVD-R writable. If it is writable, then you don’t have to do anything. Just start writing to it. But if it’s already been written to and finalized, you can’t undo it. It’s done. You need to start with a fresh one, or with one that hasn’t finalized. — Tom
What did u mean ! did u try to write an ISO file of wind8 to a dvd, ur Q is not clear here / sorry for my poor brain. Whatever u want to do regarding ur Q as Mr. Tom suggested, hope it helps u.