The issue could be resolved by doing the following:
1. Remove and unplug the unit using DIN tools (2 u-shaped tools that fit into holes on your stereo. Get them at most automotive stores) Instructions: https://youtu.be/zEyijBM1xMQ (It might require a fair bit of wiggling, unlike in the video)
2. Unscrew and remove the top metal casing plate
3. Manually remove the top disc, which should be accessible through the top of the device.
Once you replace the unit it should automatically recognize the remaining discs and allow you to use the machine as normal.
I hope this helps.