All products bundled together should have a sticker that says, "Sold As Set - Do Not Separate". There is no particular place you need to get the sticker from, but the packaging should have that sticker on it, so Amazon knows not to separate the package. Also, make sure the sticker is clearly visible.
Below is a useful link that has more information and other great shipping tips.
Amazon Packaging and prep requirements
Do multi packs need a specail sticker on them?
How do I let Amazon know I don't want my multi-pack split?
