Rule out the usual hiding places first. If the piece really is gone, check the set piece by piece
and leave with the element ID LEGO asks for, or a link to buy the part.
Technic Beam 1 x 3 ThickRedPart 32523Element 4153718×1
Trans-Red
2 pieces
Projectile, Spring Shooter Ammunition 8L BarTrans-RedPart 15303Element 6287550 or 6054526×2
Dark Red
1 piece
Large Figure Skirt, 6 Holes and Black PrintDark RedPart 28824Element 6168714×1
White
1 piece
Large Figure Armor Plate, Small with Mechanical PrintWhitePart 28220pr0001Element 6170314×1
Tick each piece as you find it, or mark it missing.
When a piece really is missing
Ask LEGO
LEGO takes requests for pieces missing from a new set through its customer service site. The form asks for
the set number and each piece's element ID, the number printed beside the piece in the parts list at the back
of the instructions. This checker lists both.
Mark a piece missing and your list links it to an eBay search for that part, which also covers pieces from
older or second-hand sets.
Keep a record
Copy or download your missing list (the CSV opens in any spreadsheet), or print the whole checklist and tick
pieces off on paper. Your marks stay in this browser, so you can check a big set over several sittings.