How to combine MLT files?

I have used Shotcut to create several MLT files. Each one combines multiple videos with various filters. I’d like to export a single long video which combines several finished MLT files. I couldn’t how to do this on Google, and I’ve tried several methods of opening or drag-dropping the MLT files with not luck. Is there any way to do this? I’m using Shotcut version 17.1.2. Thanks!

Looks like someone already figured this out!