In layout mode click on the tab you want to go to. Make sure you have clicked on the tab's name so that the actual tab object is selected. Its title should have a black border. In Inspector click on the Appearance tab and enter a meaningful name for the tab object.
Now create a script with one line: 'Get To Object ("[The name that you called the tab]")
Assign that script to a button on the layout. You will see that it takes the user to that tab. Just build that step in to a script wherever you want now.