Question: how to backup whatsapp messages from internal storage?
Answer: Download a file manager app. In the file manager app, navigate to sdcard/WhatsApp/Databases. If your data isn't stored on the SD card, you might see "internal storage" or "main storage" instead of sdcard. Rename the backup file you want to restore from msgstore-YYYY-MM-DD.1.db.crypt12 to msgstore.db.crypt12.