The Rocket League post about the Trade In update states

  • Item Trade In is a new feature that lets you choose a rarity, select five items to trade, and then be Buy Rocket League Items rewarded with a new item of the rarity you selected. This basically allows you to clean up an inventory of unwanted goods and lets you chase that item you really want.As for how the Trade In system works, you first need to have items you want to get rid of. In the April 6, 2021 update for Season 3, the Trade In screen is separated into Core Items, Tournament Items, and Blueprints – this will display how many items you have in each area and each line is broken up into rarity.

    Begin by selecting the items you want to trade from a section. When five have been selected, hit confirm to see another confirmation screen. This will tell you the items will be exchanged for one of a higher quality. Select confirm on this screen to receive your new random item.

    It’s also worth noting that you can now trade in different items from various seasons and series. The Rocket League post about the Trade In update states, “You'll have a better chance to receive an item from a Series if you Trade In more Blueprints from that same Series.” If you want something from a specific series, try trading in items from that series!The updated Trade In mechanic in Rocket League should give players more control over their items and more agency over what they want to get. Remember to keep it locked to LOLGA Shacknews for the latest news and updates about Rocket League.