Once a Nike X LEGO brick set is opened, it's no longer eligible for return, but if you discover missing or broken pieces, you can request replacements directly from the LEGO website. Here's how:

1. Start at lego.com.
2. Scroll to the bottom of the site and select "Replacement parts."
3. Select "Missing Pieces" or "Broken Pieces" and provide the required information:
   • Set name or number: You can find the set name or number on the box or building instructions.
   • Piece number: You can find the piece number on the last page of the building instructions that come with your set.
   • You'll also need to provide your name, email and delivery address.

The LEGO team will contact you if they need additional information, otherwise you'll get a delivery confirmation email when the replacement piece is headed your way.