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1. Connect your phone to your computer via USB cable.
2. On the phone, swipe down the notification panel, tap the USB icon, and make sure it's set to MTP or File Transfer.
3. On the computer, open Windows Explorer (assuming you have a PC).
4. You should see the phone listed in the devices, along with the SD card in the phone.
5. You can now use Windows Explorer to drag and drop the files from the phone's internal storage to the SD card.