Token owners who have their NFTs listed as a reserve auction are able to cancel the auction at anytime before the reserve auction has started. Once a reserve auction has begun there is no way to undo or cancel.
Instructions:
Click onto the NFTs page
Click the "Cancel Auction" button under the NFT
Confirm your auction cancellation by clicking the red "Cancel Auction"
Your wallet will prompt you to confirm a gas fee to complete the process.
You will see a confirmation screen to confirm your auction has been cancelled.