How to control mbot(atmega2560)'s dc motors and leds using Form app ?

Hello,
For the STEM project, I want to implement a form using c # so that children can control mBot's DCengines. This program only needs to be forward, backward, right, left and for how many seconds. How do I make the connection between the robot's engines and the form application using c# and how can i code arduino part?

I can connect the robot with a cable and select the port to which the robot is connected using c#, but that's it.

Also asked at (with C# code):
https://stackoverflow.com/questions/57338126

If you're willing to add bluetooth to the project I'd reccomend using MIT appinventor to just build a simple app on your phone. It's really easy to use and creates functional apps.