In order to view and fill out your form offline, it is crucial that you first ensure that you have loaded the form onto your mobile device by logging into your account (while connected to the internet) beforehand. This will allow to download all the forms in your library as well as update any current forms.
Once this has been done, you can login to your account in "Offline Mode" to launch the app, view, and fill out forms. When you try to submit your forms while in Offline Mode it will put your completed forms into a "Sync" folder on your device. Once you have an internet connection, whether via WiFi or Mobile Data, your device should automatically sync all forms in this folder. If your device doesn't auto sync then you can manually sync the folder from the device, you can do this with the button in the top right corner of the "Sync" folder.