The guarantee only helps if you can claim it. A little preparation makes that easier.
Your order number, the email used, the purchase date and the pack you bought. A short, polite request stating you are asking for a refund under the 60-day guarantee. Photos of the bottles if there is any issue with them.
The page does not list a step-by-step process, so check the refund policy page and the contact page.
Send your request in writing well before day 60 and keep a copy. Note the date and ask for confirmation of receipt and the next steps. Follow any instructions on returning bottles exactly. Screenshot the policy as it read when you ordered.