If the campaign is still ongoing, you can cancel your donation and make a new one, this time selecting the desired reward. To cancel a donation, you must be logged in on the website. Click on your username on the top right corner of the website and then on the “My transactions” tab. Click on the “cancel” icon (the crossed circle icon). You will get your funds back within 72 working hours (preapproved transactions like PayPal will simply not happen).
You can also decide to contact the project owner and explain you want a different reward (if you forgot to select a reward and would like one for example). Use the link “Send a message” in the Creator box on the right part of the campaign page.
If the campaign is over, you must contact the project owner to solve the issue.