How can I get this "x" button on tab in the run mode.
Currently I can only see it in design mode not in run mode.
The 'x' and '+' button on the Tab Container are only available in the Designer as a tool to delete and add tabs while editing your project.
Once you run your project the tabs you have are set (unless you have some sort of script or binding writing to the tabs property) and those buttons will not appear.