after downgrade from iOS 14 to iOS 13 on I phone I am not able to restore the back up. its says Could not restore the. iPhone “Sagar iPhone” because the backup was not compatible with the iPhone that is being restored. SO HOW DO I FIX IT

Having 13.7 shouldn't matter. In theory, you should be able to restore backups within the same major iOS release set. Did you backup to your Mac or to iCloud?

Regardless, see if the following article can help:

• If you can't back up to iCloud or restore from iCloud backup failed - Apple Support

Hello sagardhl10,

We understand that you're having some difficulty restoring a backup to your iPhone, and we'd like to get you pointed in the right direction for an answer. Get started here: How to uninstall iOS beta software

This article will walk you through everything you need to get your device on the latest version of iOS 13. Please note that backups created while using beta software might not be compatible, however, if you made an archived backup you can still use that. Complete steps to restore a backup to your iPhone can be seen here: Restore your iPhone, iPad, or iPod touch from a backup

We hope this helps answer any questions you have.

Take care!

Ok, see if this article helps:

• If you can't back up your iOS or iPadOS device to a computer or restore it from a backup - Apple Support

Per chance did you use a backup that was created AFTER you upgraded this iPhone to the iOS 14 beta? If so, then it will not be compatible with the iOS 13 firmware and cannot be used to restore your phone's data. You would need a previous backup that was made when the phone was still running iOS 13.