I made a 2D simulation which has x and y coordinate, and did not set up any value for the z coordinate. Do you know what is the build in value of the z coordinate?
I recommend checking the manuals for this operation. You can get them using the official website of the developer, but the only thing that's required is a username and password which you should have since you're using their software. I have tried to get the solution from other sources, but I couldn't find anything particular.
Support page: https://dynamic.silvaco.com/dynamicweb/silen/