I use an iPhone 4S , I have an application called whatsapp I want to to able to lock its conversation private to me alone , keeping it away from prying eyes so ,please how do I lock my conversations

How to spy on WhatsApp messages from Pc or mobile Android and iPhone

OPTION 1: Restore WhatsApp Messages Locally

Step 1: The very first solution to your problem is to restore it locally by UNINSTALLING the WhatsApp Application on your device.
Step 2: REINSTALL it again.
Step 3: SIGN IN YOUR ACCOUNT in the newly installed application. Then, you will be prompted with a message that says, you are able to restore your backup after reinstalling the application on your device.
Step 4: All you need is to press RESTORE and your problem will be gone. But you need to keep in mind that the backup for your WhatsApp history is only valid for 7 days and after a week, it will be gone and you will not be able to locally solve the problem.

OPTION 2: Retrieving Deleted WhatsApp Messages by A Data Recovery Software

Step 1: CONNECT YOUR MOBILE TO YOUR COMPUTER WITH A USB CABLE
Step 2: ENABLE USB DEBUGGING THROUGH SETTING UP YOUR MOBILE PHONE
Step 3: Choose the mode according to the operating system. Like this: android 2.3 or earlier, enter SETTINGS and click APPLICATIONS then click DEVELOPMENT and tick USB DEBUGGING
Step 4: Next step that you should take is: SCAN AND ANALYZE THE DATA ON YOUR MOBILE.
Step 5: Lastly, you have to TAKE A LOOK AND RECOVER FILES FROM WHATSAPP HISTORY.

OPTION 3: Use FoneDog - Android Data Recovery to Recover Deleted WhatsApp Messages

Step 1: Download and Install
Step 2: Select File Type

Step 3: Select Mode
Step 4: Select Files of WhatsApp Messages from Android to recover

Video Guide: How to Recover Deleted WhatsApp Messages From Android Phones
More refer:
How to Recover Deleted WhatsApp Messages on Android
How to Restore Deleted WhatsApp Messages on iPhone

latest version of whatsapp for iOS 4.3 and up is 2.11.16
For speech use Skype to Tango. Needs iOS 6.0 or up and has version 3.15.139973

Plug your iPhone into a USB connection on your PC. Give it a minute.

- Your iPhone will ask if you want to allow this device (your PC) to access your photos. Click ALLOW.
- Go into Windows Explorer and your iPhone will be there. - Click on it and there will be a DCIM folder. Click on that folder.
- You will find one or more folders under DCIM. Each of these contain the photos on your iPhone.
- COPY (DO NOT MOVE) these from your iPhone to your Computer's desktop. Now you have all photos on your computer and you can safely wrestle with restoring your iPhone.
I hope this response helps you out.
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Restart your phone by holding down your Home Button and your Lock Button at the same time for about 10 seconds or until you see the apple logo. This will restart your phone and should resolve your problem!