Within your account, you can set default Reading Options, which will be applied to all new titles when they are created. These default options will automatically be applied when content (PDF or epub files) is either uploaded directly or imported from the INBOX at ftp.netgalley.com. You can always change the reading options for an individual title record from the TITLE DETAILS page (for example, if you usually enable Kindle, but have an image-heavy file).
To do so, click your Publisher Name at the top of the account (next to the silhouette icon). In the side-bar at the left, look for "Defaults for New Titles" and click the orange arrow next to "Reading Options"