How can i change my item to eternalized

I want to change to eternalized to drop eternal which stone i need?

You can’t, eternal items can only be dropped.
The max you can do is to improve an item’s quality to 25%, but eternals have 50% quality.

But if you are talking about the set (green affix), you also can’t roll it with a crystal.
But you can drop those items on floor 350+.