Download the cosmetic that you wish to use from the Steam Workshop make sure it's for TF2.

• Click the plus button and then "Create Animation Set for New Model" load your cosmetic.

• Select your character (Not your cosmetic) drag your character over your cosmetic to lock it to your target.

• Now pick only the locked bones you will know what bones are locked because they have a lock icon besides their name.

• After you have selected your locked bones drag the default, zero, half or one slider until your cosmetic is properly placed.

• To move your cosmetic item you will have to drag your character as you would normally do.