The other response is correct that this is not something you can directly do in Studio, but the Screen Recorder can quite easily.
You would first need to download both videos from Studio so you have the MP4 files.
Go to Record -> Screen Capture and simply record a couple of seconds to get into the recorder.
Then go into back to video projects in the upper left of the recorder.
You will notice a button in the upper right that says Import
You will then import in each of the videos you want to combine. You can then go in to edit one of the videos.
In the editor there is a tool on the bar that is under Insert which is Existing Recording. Once you click, it you simply place the cursor where you want and it will combine the videos there.
From there you click done and then can Upload that new combined video directly into your studio.
I hope this helps!
Thank you for providing those directions. It's been a while since I used that interface, but your instructions do sound correct.
I'd also note that, in my experience, you need to be working on the same computer when editing videos using that online tool. In my previous position as a Canvas administrator, I had found that I could not edit (or really even find) my videos using my home laptop when I had been working on the videos using my work laptop. It seemed like everything was saved locally to the laptop hard drive before it was uploaded to the Studio library.
Thanks again for providing this information!