Default Layouts can be configured using the "Layout Editor" under "Options". You can then go to "Layout" and click and drag the search tab to the first slot in the tab panel. If there is no option to edit, you can click "Copy" to create a new Layout and then move the search tab to the first spot of the tab panel.
If you had to copy the layout, after saving, make sure to set the new copy as your "Default Layout" so it will be the layout that opens when you start the DTS Editor. You can do this on the "Layout Editor" by clicking "Configure" in the top right corner of the Layout Editor panel, and select "Set Default Layout".
Let me know if you have any questions or if there is anything else I can help you with.