Use your device's file browser* to find the Move to iOS installer with filename ending in .apk. On many devices, you'll find this .apk file in a downloads folder.
Tap the file to install it.
If an alert says to change your security settings to let you install from unknown sources, follow the onscreen steps. After you change your settings, you might need to tap a back button to return to the file browser. Then you'll be able to install the .apk file.
* If you don't have a file-system explorer, search for one in an app store for Android apps.
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