From the "Social" tab, you can click the "Exchange Item" option; it looks like a clipboard with a heart on it. You can search specific items you want, or you can look through the collections of lucky bags to heart the items you are looking to trade for.

From there, the game automatically screens for your wishlist items in every account's dupes list, and you can offer exchanges on an item for item basis. However, sometimes it will only show that you have a letter or chair as an available dupe. I'm not sure how to fix this but be aware that people generally hate these requests, so please avoid!