How can I retrieve accidentally deleted data on iPhone?

You cannot recover any data that existed only on the iPhone itself. Resetting (not merely restarting) the phone would have wiped it.

Do you have any iCloud backups or other backups? Were you synchronizing any data to iCloud?

“Loss iphone data recovery: By mistake restart device and my all data deleted please recovery data”

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Deleted Files After a Restart:

Look in Drafts:

What are the items? For Mail, look in Drafts, and see if they reside. And do the same for all other apps that have the feature for Drafts.