How to add socket(s)

I removed a normal affix from one of my legendary items in hopes of replacing it; the affix was removed, but not i can’t figure out how to replace it, as there is no empty socket, and I can’t figure out how to add a socket. I’m guessing this has been asked/answered before and, if so, i’m sorry if this is redundant, but I can’t seem to find the answer with the search function.

You need to apply a Zircon Crystal.