At this time, dual extrusion on SeeMeCNC printers is highly experimental.

Here is the download: Firmware

Run an EEPROM Clear Sketch, Located in the Arduino software under File>Examples

Configure Firmware: Since this is highly experimental at this point in time, the default configuration is pre-equipped for Rostock Max v3. If you are installing this system on a machine other than a Rostock Max v3 you can change configurations here in the configuration.h tab of the firmware.

You will need to change the defaults to match your printer model and equipment. FOR DUAL EXTRUSION YOU WILL NEED TO CHANGE THE "#define NUM_EXTRUDER" FROM 1 TO 2

Upload the firmware when you are confident that you completed configuration changes.