Plugin Help Iventory ItemMeta Updating

Okay this is what I'm doing.
I have a plugin that has a custom inventory that has items that represent weapons. when a player hovers over said item the meta has " █ █ █ █ █ " those are level ups and to start off they are all gray. Meaning that they haven't upgraded i. When a player has a certain amount of money they will be able to click this item and then the item meta for only this person in this inventory will have one of those blocks are green. Now I kinda know how to update it but what happens is I want it to show right after they close that inventory.