Here's how to create a backup and restore it.
1- Open WhatsApp >> Settings >> Media Settings >> Backup conversations
2- This file will be saved as "messageStore-YYYY-MM-DD.1.db.crypt" in the /device/misc/whatsapp/backup folder on your BlackBerry 10 smartphone. WhatsApp recommends that you saved this file as "messageStore-YYYY-MM-DD.1.db.crypt.current" so that you don't have trouble finding it.
3- Now uninstall WhatsApp. Make sure that you know the name of the correct backup file
4- Reinstall WhatsApp. After verifying your phone number, select Restore and pick the correct backup file.
5- If you are using BlackBerry 7 smartphone, you need a microSD card to backup chat history. This is because message history is removed from the internal storage after restarting BlackBerry 7 phones. If you have a microSD card in your phone, here's how to back up conversations.
5-1- Open WhatsApp >> Settings >> Media Settings >> Message History >> Media Card.
(This ensures that all your messages are saved on the memory card).
5-2- If your chats have stopped showing up in the app, uninstall WhatsApp.
5-3- Switch off the phone, remove and replace the battery. Restart the phone
5-4- Open your BlackBerry Media folder, press the BlackBerry button >> Explore
5-5- Open Media Card >> Database >> WhatsApp and look for the "messagestore.db" file.
5-6- Rename it to "123messagestore.db". This will ensure that WhatsApp restore the next most recent chat history that was saved.