Hi there kavitha1977,
Thanks for reaching out to Apple Support Communities. We understand you're having difficulties restoring your device and see you came to us from a helpful support article. Were you able to fully work through the troubleshooting steps listed to try to resolve? If so and you're still having difficulties, it's likely that the iTunes version that you're running on your computer no longer supports the old iOS version that's running on your iPhone 4, as this device was released over 10 years ago. In this case, you may want to reach out to Apple Authorized Service Provider and see if they are able to assist with restoring your device.
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Best regards.