Entity Holding Item?

In my mod, I'm trying to make an entity similar to the Allay, where i want it to fly around and hold items. I got the flying part done, but i still need it to hold items.

I want to have it so when you hold an item and give it to the mob, then the mob will hold it, and if your hand is empty and the mob is holding an item, then you will take it from the mob.

I cannot seem to have it hold items. If it matters I'm using a Geckolib Animated Entity.