Search for the "Samsung GT-C3520 Stock ROM" matching your region's language pack. The file usually comes in a .zip or .rar archive containing the BIFF or BIN data.
Verify you are holding the correct boot key combination while plugging in the cable. samsung gt-c3520 flash file and tool
Flashing erases all personal data, contacts, and messages. Search for the "Samsung GT-C3520 Stock ROM" matching