Dual extruder using both filaments for a single print

When I load a model into Luban I can select either the left or right nozzle but the Both option is grayed out. Is there a way to actually have Luban alternate between the two colors or is that something I have to do to the model prior to loading. I’m new to this and confused at how I can actually use both colors in a single model. Thanks for any help.

For dual colour, you need to slice your model into more than one piece, then it would be possible to select one piece for extruder one and the other with extruder two.

There is painting app, which should do the same but not sure right now:
SimplyColor3D 2.0 - Convert any 3D model into MultiColor,
https://www.kickstarter.com/projects/bigbrain3d/simplycolor3d-20-convert-any-3d-model-into-multicolor?ref=android_project_share

Here are multi colour able models:

Thanks for the tip. I’m not experienced at generating my own 3D models nor slicing them. I’ll try the SimplyColor3d app. Really appreciate the quick response.