You need to go to the email you received after placing an order, then click on the link you received that says “Manage Subscription" Click here. From there, you will be able to add your products, change the delivery date, the order frequency, your billing info or even cancel your subscription. 

Alternatively, you can also go to your Swiss Toniq account by logging in using your username and password Click here, then click on “Manage Subscription » Click here 

You can swap products on your Manage Subscription page. Click on the "See more details" button to view your susbcription; 
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You will see the Swap product button at the bottom of the product name: 
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Select the product you want to swap and click on "confirm swap". 

Should you have further questions, please do not hesitate to reach out. Thank you