Q: How can I pair my apple watch with same iphone that was already paired but was restored?

When did you save the backup you restored to? If you paired the iPhone with your Apple Watch after the backup it will still be paired. If not, you will have to repair your Apple Watch with your iPhone. Unpair your Apple Watch first by resetting the device (Unpair your Apple Watch and iPhone - Apple Support) and repair it with the Watch app on your iPhone. Just know, when resetting, you will still have your data except if it was saved locally on your Watch (synced photos and music, or native watchOS apps)