[2021] How am I supposed to get the 9th decal from Operation W.I.N.T.E.R., if I got a duplicate?

Hello

As with most event decals, they can be traded on the marketplace. Any duplicates you receive can be traded on the market and any ones you are missing from your collection can also be obtained from the market.

The 9th decal is awarded on completion of the collection, as per most decal collections, such as the major update decals and many others.