If you have accidentally deleted an important note in the Notes app, then all is not lost. Chances are that the deleted note is still present the device.
You don't have to purchase expensive apps or go through complex procedures; iOS 9 is shipped with a revamped version of the Notes app that keeps your deleted notes in a special folder. Deleted notes are kept for a period 30 days before they are permanently erased.
How To Recover Deleted Notes on the iPhone, iPad and iPod Touch
Open the Notes app and then tap on the small < button to switch to Folders view. Go to On my iPhone > Recently Deleted. All the notes you’ve deleted during the past 30 days are listed there.
Select the desired note and then tap on the Edit menu > Move to…. Transfer the note back to your main Notes folder or iCloud.