It’s a fairly common situation. You buy a new iPhone, but still, use the old Apple Watch. It can be tricky to do because Apple Watch doesn’t really sync to the iCloud for backup files. Apple Watch borrows the information from the paired iPhone, which has its data backed up in the iCloud. If you recently bought a new iPhone, syncing it with the Apple Watch is easy. Since iOS 11.2, you can use the Automatic Setup feature to move back up to the new iPhone with repairing or unpairing. It is important to make sure that the iPhone is moved properly to the smartwatch. Do the following:
Enable the iCloud Health Sync to make sure that your Apple Watch is up to date
Make a backup of the old iPhone before transferring it the new iPhone
If you choose not to restore from the backup of the old iPhone, you need to force the backup. Unpair the smartwatch from the old iPhone. Be sure that the Health data has been enabled before syncing in iCloud. Alternatively, you can choose the Automatic Setup guide. There would be a prompt saying “Do you want to use (name of Apple Watch) with this iPhone?” and press Continue.
After unpairing the old iPhone with the smartwatch, set up the account of your new iPhone in iCloud. Once you finish the setup process, bring the new iPhone to the Apple Watch. A pairing screen will appear and the Watch app will open. Be aware that you could permanently lose health data if you don’t enable the iCloud health syncing.
If you have an Apple Watch with LTE support, it is important to make sure that the data connectivity works. If you have a brand-new iPhone, it is not necessary to move the data plan. If you still use the same phone number for the new iPhone, your data plan will not change, even if you get a brand-new SIM card as well. However, you may decide to change to a new carrier and it means, you need to subscribe to a new data plan. Follow the carrier’s instruction to set up the new data plan on your new iPhone unit.
Some people want to start from scratch with their brand-new iPhone without any backup. If you don’t mind losing the Health data and other information, just start from scratch on the new iPhone and Apple Watch. You will also lose achievement, heart rate data, GPS route, saved workouts and downloaded apps. If you prefer to keep the health data, transfer them to the smartwatch and clean-install iPhone. Go to Settings> iCloud and enable Health. You need to wait for a while if you have plenty of data in the backup. Once you sync the Health information, unpair the Watch with old iPhone and set up the new iPhone. Open the Watch app on the smartwatch and follow the instruction to pair it with the brand-new iPhone. If all works well, you should be able to use the Apple Watch as usual.