If you're unable to find the Submit to Turnitin option when attempting to upload from a third-party app, it's likely that you need to enable it.
- Navigate to the share/send copy area of the third-party app from which you are submitting.
- Found to the right of the list of apps that you may share your document to, tap the More (...) icon.
- From the Activities box, tap the Submit to Turnitin toggle, switching it to green, then select Done from the top right-hand corner.
- Tap the Submit to Turnitin icon to proceed with your submission.