In this case, the game means disk 2 when it says data disk (you can assume the disk label on the original disk says “Data Disk”). And the internal drive is the first floppy drive. So you need to use the F12 menu and change the disk in the first drive (from disk 1 to disk 2). Before starting the game, you should ensure both game disks are added to the floppy swap list as explained on this page.
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