There's a "help" link on the top of ebay pages.
Type "retract a bid" and this comes up
If you've made a mistake when bidding on an item, you can retract your bid in certain circumstances.
Are you a seller looking to cancel a bid? Read our article on canceling a buyer's bid
Whenever you place a bid, you're agreeing to buy the item if you win the auction. However, in some situations you can retract your bid.
Retract a bid
Keep in mind that you can't always retract a bid once it's made – if you're not able to retract your bid, you can also try contacting the seller to see if they'll cancel your bid for you.