There are a few ways of moving items around within a reading list:
The Move to Clipboard feature is useful if you need to move an item to another section entirely. Click on the three-dots on any citation, and select 'Move item':
Then select 'To clipboard':
A clipboard icon will appear on the right of the list:
Navigate to the section of the list where you want the item to be moved. Click on the Clipboard icon, and drag the item into place on the list, using the horizontal bar to position: