I ignored the update pop-up too many times and cant seem to access an updated version of Discovery mode. Is there an option to get this update link?
Would you please give us a more detailed explanation of the pop-up? You should be able to use Pix4Dmapper even if it is not the latest version, so I am not sure if it is the reason why you cannot access it. In any case, firstly, I recommend completely uninstalling and reinstalling to see if it works.