If your reports are sharing to another app by default, you will need to go to your Device Settings > Apps and then find the app that Site Audit Pro is currently sharing to. For example, if you're currently sharing to WhatsApp by default, you will need to find WhatsApp in that list. Once there, tap on the "Clear Defaults" button to reset this option.
If your reports are sharing to a device such as a Printer, you will need to go to your Device Settings > Apps. Tap the overflow menu in the top right. When it opens, select "Reset App Preferences". This will reset all defaults across your device but unfortunately this is the only way to reset an app sharing to a printer by default.