Inventory was full when picking up a quest item. Now the item has disappeared and I can’t complete my quest.

Has anyone run into this and figured out how to fix it? I haven’t played in weeks because of this and I miss it! I’ve tried looking through other posts and it seems like others have had this problem but they don’t say how to fix it. Please help! The item is in Wall-E’s house.

Edit: I’m playing on the Switch.