Transferring to iOS from Another Platform
As of June 20th of 2018, Pleco licenses are no longer platform-specific, so to activate an Android purchase of Pleco on iOS, simply copy down the “Registration ID” from the Pleco “Registration” screen on your Android device and enter it in the same screen on your iOS device. (you can access that screen via the sidebar menu)
If you bought Pleco on an old Palm or Windows Mobile phone, go to My Orders and you can have your Registration ID from that purchase emailed to you from there.
To migrate flashcards from your Android device to iOS, see this page for instructions on how to back them up on Android and this page for instructions on how to restore them on iOS.