XMind doesn't support synchronization. If you want to open the mind maps created with your iPhone/iPad on your Android phone, you may need to transfer your mind maps to your Android phone.
1. Wi-Fi Transfer
1) Make your iPhone/iPad and Android device connect the same Wi-Fi;
2) Launch XMind for Android;
3) Tap "three dots" > Wi-Fi Transfer, and then you can get an URL to connect two devices;
4) Launch Safari on your iPhone/iPad, go to the URL shown on XMind for Android;
5) Tap Upload files > Browse;
6) Tap an .xmind file and then it will be uploaded to XMind for Android automatically.
2. Transfer files via a third-party cloud service
(OneDrive as an example)
1) Launch XMind for iOS on your iPhone/iPad;
2) Go to Browse > Location > OneDrive > save your mind maps into OneDrive;
3) Download OneDrive APP on your Android phone and sign into your OneDrive account;
4) Launch XMind for Android;
5) Tap "three dots" > Import;
6) Tap the menu icon on the upper left corner;
7) Enter OneDrive and select an .xmind file to import it into XMind for Android.