To withdraw an application you need to press the withdraw button in your application. Go to My applications, pick the application you want to withdraw and once you're in the application look for the withdraw button in the right side of the cover picture.
When you press withdraw in an application you'll see this prompt message that confirms you are sure of withdrawing.
If you withdraw the application, you won't be able to apply for that opportunity again in the future. We recommend you to search for similar opportunities in the location you're interested as we have plenty of them.