To withdraw a bid on eBay, you need to log in to your account and go to the help and contact page. There, you can search for "retract a bid" and click on the article or the blue button that leads you to the bid cancellation page. You can then choose the bid you want to cancel, type your reason, and click retract. You have to meet eBay's bid canceling rules and criteria, or your bid will not be retracted.