Xmind for Android doesn't support synchronization at this time. You need to transfer your mind maps from your Android device to your iPhone/iPad.
1. Wi-Fi Transfer
1) Make your Android device and iPhone/iPad connect with the same Wi-Fi;
2) Tap "..." on the upper right corner of the main page on Xmind for Android;
3) Tap "Wi-Fi Transfer" and you can see a web address;
4) Launch Safari on your iPhone/iPad;
5) Input and visit the address shown on Wi-Fi Transfer;
6) You can tap any mind map to download it to your iPhone/iPad.
2. Transfer via A Third-party Cloud Service
1) Go to internal storage > Xmind > workbook on your Android device to find your mind maps created with Xmind for Android;
2) Upload the .xmind files to a third-party cloud service, like iCloud or OneDrive;
3) Launch Xmind for iOS on your iPhone/iPad;
4) Go to Browse > Locations > cloud drive to find your mind maps.