Open WhatsApp
Verify the same phone number and Google account on Android or iCloud account on iPhone
Uninstall WhatsApp
Reinstall WhatsApp from the app store
Open WhatsApp and verify your phone number
Tap Restore when prompted
Wait for the chat backup to finish restoring
Tap Next
Wait for media to restore after chats appear
Ensure backups are enabled for future restores
On Android: WhatsApp Settings > Chats > Chat backup
On iPhone: WhatsApp Settings > Chats > Chat Backup