I literally just copied this from the help page lol:
Once you are logged into your account, look on the left side of the screen and click on Saved Shipping Addresses. 2) Once on the Shipping Addresses page, enter in your address into each box, then click the Validate Address button. 3) Your address will be formatted and displayed on the right side of the page. Double check to make sure everything appears correctly. If so, mark Yes and then click on Save Address. 4) If your address is NOT correct, mark No, click on Save Address and follow the tips to verify your address. If your address still is incorrect, submit your address for review and we will assist with it as soon as possible. 5) Congratulations! Your address is now verified and saved in your account! You can now send your verified address to sellers after you’ve won their listing. 6) If your address is NOT correct, mark No, click on Save Address and edit your address. (Please note that if your address continues to appear incorrectly, save the address anyway, even if it's not correct, then submit a support ticket for further assistance.)