- Within the Startup VI of your executable click File >> VI Properties...
- Choose the Window Run-Time Position option in the Category dropdown menu.
- Change the Position dropdown menu to Centered.
- Build your executable as normal.
If you'd like your application to automatically center itself without having to click the run button, you have to select the "Run when opened" option within the Source File Settings. See this link for more information: Why Doesn't My LabVIEW Executable Run Automatically When Opened?
There is no way to center the window automatically upon opening without automatically running the executable.