How you start the GUI depends on how you installed it.
Did you install the chocolatey package? Chocolatey will have installed a small stub program to run the GUI. In that case just type
If you added the install directory to the path, just type
Otherwise, use the path to which the GUI was installed:
<path to the install directory>\testcentric.exe (*)
(*) Of course, you would use a forward slash on Linux.