When applicants are working in the application they can click the next button to move forward. However, if they wish to return to the previous page to make a correction or review something they input, they must scroll to the top of the screen and select the tab. For flexibility when moving around in the application you should be able to select next or previous.
This functionality is now available with latest updates to the Applicant and Grantee Portal. https://community.blackbaud.com/blogs/108/9692