How do I open the casing?

use a big suction cup to lift the bottom plate up so you will not damage the casing. this is what the official apple service manual says

Without the suction cup, there are three simple snap tabs on either side of the case which can be pushed back with playing cards to open the case. You then need a Torx 10 and Phillips #00 or #000 drivers to remove three screws which hold down the drive in the case. After pivoting the drive up, you need to remove the two side Torx screws that fasten a mounting plate and 4 small Phillips screws to lift up the top plate and remove the stuck disk.

I was going to grant access to the paperclip eject hole I expected to find, but THERE IS NONE! If software won’t eject a disk in this drive, there is no option but DISASSEMBLY!

Jim