Are you trying to make UGC accessories and want to try them on in-game? Here is how!
With my accessory test dummy its very easy.
First, get my model from this link
Try-On Accessories Equip with Proximity Prompt - (roblox.com)
Next place the model in your baseplate from the toolbox
Then take your accessory and in the Explorer drag it on to “Try on Accessories!”
Now that it’s on the avatar, press the play button
When you walk up to the avatar, it will give you a prompt to “Interact”. Press the prompt and it will equip your accessory.
This works with any accessories, not just hats! Now you can see your accessory exactly like you would in any game.