If I get it right, you want two slideshows to play on the screen at the same time. You can do it like this:
1. Create two slideshows and convert them into two separate videos
2. Start a new project and add one of the videos to the storyboard
3. Open the slide editor and go to Add Layer > Video to add the second slideshow
4. Resize and position the videos as you need https://prnt.sc/21jn14j
You can also crop the videos to get the shape you need. https://prnt.sc/21jn97d

If you mean something a bit different, you can explain it to the customer service and they'll give you an instruction on how to do this: https://smartshow-software.com/support.php