You are just giving some assets to vendor and after perform the process of material, you are taking the assets back. Is there any losses of the assets at vendor location ? Are you giving/taking any charges for the assets from the vendor ?
If there are nothing about changes and it just managed with quantity, then you can just use the movement type 541 and 542. 541 will be used to transfer the material from your storage location to vendor and when vendor will return the assets to you, then perform 542 movement type vendor to your storage location.
Use the material type as per your asset material (valuate or non-valuate).