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If you have deleted any note and want to retrieve it then you can retrieve it but you should not have deleted it permanently. To retrieve it you should go to recycle bin and open the file which was deleted and right click on that and tap on the restore option.after that file will be back to its initial folder.
If you permanently deleted it, you can restore it from iTunes, if you have a backup there.
Connect your iPhone to the computer.
Right-click on your device and press ‘Restore from backup…’
Choose the latest backup and proceed.
If you have a backup on iCloud
follow these steps to restore from iCloud.
First tap into home page
From there tap on setting option.
Then press the iCloud option.
Now sign into iCloud account with your id and password.
After then Select the backup and storage button.
At last tap to done option.
If you do not have backup on iTunes and iCloud, you can try the following third party tools. They claims they can recover deleted notes also. But I do not have experience with these apps. SO I recommend you to try their trial versions first. Data Recovery for iPhoneWoundershare data recovery application