The Corsair Obsidian 800D case comes with four external 3.5 inch drive bays hidden behind a door on the lower part of the front bezel. Unfortunately they are hot swappable drive bays. Each of the 4 hot swappable drive bays has a small circuit board behind it where you connect a SATA cable and a SATA power cable. The bays are not intended for use with floppy drives.
There is no adapter plate visible in the photo of the case which shows components and accessories.
Floppy drives are becoming obsolete. They are no longer required in modern systems.