If you have changed mobile device and you’d like to download your Synthesis App again (provided that you had already purchased it), you need to open your new phone, sign into the App or Play Store, search for “Synthesis repertory Schroyens” and download the app again.
If you transfer everything from one phone to the other normally you will not need to do this because the phone’s backup will take across all of the existing apps.
If you change from an iPhone to an android phone (or vice versa), you will lose all of your apps, and you’ll have to purchase everything again. Unfortunately the 2 companies don’t allow app transfers, and there is nothing that we can do about it.