Hello, Matt. Thank you very much for reply.

That's exactly what happened. After regenerated, I lost all of my hard work..........
That's why I wanted to make the specific bass line using soloist track.

Well, I've just solved my problem!

The thing is...
I didn't know how I can make the empty soloist track to the bass track on notation mode, and I was struggling putting the low notes in the bass clef.
All the higher notes went to the treble clef, if you know what I mean.

But I tried some setting changes in the option dialogue, and voila!

I am so happy!
This is really great!

Thank you guys!