There are several ways to merge parts and/or tracks with Cubase.
As previous posts have suggested, you can drag parts from one track to another. You can expand tracks that have multiple parts stacked into lanes.
Questions to answer…
Do both tracks speak to the same instrument and channel?
If not, do you want to force it all to use the same MIDI channel, or do you wish to keep the channels independent even though they now share a single Cubase ‘track’?
Do you have real time options set up for either or both track in the track inspector? If so, do you want to freeze these first before merging? Remember, if you merge MIDI tracks together, you’ll now be stuck with one set of ‘real time’ transforming tools.
Here’s an example…
Lets imagine a scenario where you’ve split your MIDI controller to record your left hand playing up to middle C on channel 2 of one track, and the right hand along with your pedaling CCs on channel 1 of another track.
You might first set the real time transformer stuff you desire in the track inspector of each track and freeze it first. This will force everything ‘real time’ to be hard coded into the part.
Then merge the two tracks together on a new track that is set ‘channel any’. With the output channel of the track set to any, then your right hand stuff will still go out to your instrument/plugin over channel 2, and your right hand stuff over channel 1.
Then you might change the output channel on your new merged track so it all goes to channel 1 into your MIDI instrument/plugin.
Mute your original channels and test your new track. Once satisfied it did what you want, get rid of the old source tracks.
Within the part, the left hand events would still be designated as channel 2, while your right hand and pedaling CCs would still be designated as channel 1. As it gets output for play back, it all goes out over channel 1.
Why would you want to do this? The score editor assigns score ‘voices’ according to MIDI channel.
In short, check out the links I’ve embedded above for lanes, freezing midi modifiers, and merging MIDI/Instrument tracks.