If you need to contact Pottermore to report a glitch you've been encountering, or just want to give general feedback, you must scroll down to the site's footer and click on the 'Help' link.
Click on 'Other' from the list that will be provided then scroll down and click on the tab that reads 'What's Next?'
At the bottom of the tab, below the paragraph, there is a link that says: 'Need more help?'
Click on this to make the feedback form apear.