I wanted to know if there was any way I could reset a Roland D-20 back to all its original settings.
The Roland D-20 can be reset by following this procedure:
HOLD TUNE/FUNCTION AND WRITE WHILE POWERING ON.
According to a synth reset guide page.
If you need the factory patches, they exist as .MID files here:
You can dump them into your D20 with any freeware MIDI sequencer and a MIDI interface.