Hey Bricks! Sorry I wasn't able to get back to you sooner. I've been busy lately. To answer your question. There are several ways you can unselect the item/equipment you choose:
1.) Simply select another item/equipment to unselect the previous one but you will be holding another one
2.) I haven't tested this one out but in principle all you need to do is add a TRUE/FALSE event on the A button. Add a variable that when you select item/equipment 1 then item/equipment 1 is TRUE and if FALSE add the event animation state back to default. So that when you add a TRUE/FALSE event on the A button it will toggle that if player is holding item/equipment 1 it will know if it will go back n forth to whichever animation state. It's quite complex. Which is why this is just a basic system.
3.) Add an item box or equipment box of an icon of a fist meaning he wont be holding anything when you click it. But you have to change animation state to default so let's say Box 1 is a sword, Box 2 is Pickaxe then Box 3 is a fist which means unequip. Not sure if that made sense but yeah.
So far those are the solutions I can think of, you might have to tinker with it more because I cannot do that as of the moment. Will look into it more and maybe I can guide you later on. Sorry about that, it's really just a basic system that I made that isn't super complete because the idea is for everyone to be able to customize their own. But nevertheless thanks for your support!