Select your player and add the InventoryPlayer component to it. Once added you'll have to assign the character window that belongs to that player (leave empty when not using a character window), the inventories that belong to this player, and the player's skillbar.
Once the character window is assigned you can hit the "Force re-scan" button; This will load the CharacterUI's equipment fields and allow you to bind them to a player's bone.
For example, you have the equippable field "Head" in your CharacterUI, once you've hit the Force re-scan the "Head" field will appear in the equipment binding list. Here you can then associate a bone with this equipment location.