Hi, I am making a magic item that can cast both shield and Destructive wave once before having to take a long rest, and that's where the issue comes in. I don't know how to make to only be used once before having to take a long rest to reset it. I have given it charges, but that hasn't been working, I would like to know how to make it the way I have it if there is a way to do it. 

What you want is impossible. You can either give them two magic items, each with one spell and a single charge, or you can put both spells on the same item with two charges and the player gets to choose how to spend those charges.