You’re almost there. Now, your boxes are ready and you just need to either (a) drop the boxes off at UPS, or (b) schedule a pickup.
This part is handled off of Amazon / Seller Central.
You have two options, either:
Look for the nearest UPS access point (https://www.ups.com/us/en/business-solutions/expand-your-online-business/ups-access-point). You can go to the access point and drop off the boxes there directly.
Call 1-800-782-7892 to schedule a UPS pickup. If you do not already have a UPS shipping account, you can create one (https://www.ups.com/us/en/business-solutions/open-an-account) to access discounts.
That’s it! Now all you have to do is wait for Amazon to receive the boxes, and you’ll see an update on your inventory inside Seller Central.