how can i retrieve part of a note i accidently deleted . the note is there but the part i deleted is what i need

Shake (rather forcefully) the iPhone to be offered to undo the changes. The “shaking” functionality is the common way to undo several things on the iPhone. Note that if you moved away from the note, this functionality won’t work.

If all you did was to delete a specific section of text and not the entire text, there is no way to restore that text except to restore the entire note from your latest backup. However, restoring a backup means restoring everything to the state it was in for your last backup. So if you have an older backup, that could mean more information could be deleted. There is no way to undo the delete or recover just a text message backup.