MAIN TABS (the top row) Illustration below Tab1 shows no MAIN TABS identified same for SUBTAB
Figure 1 – MAIN  TABS  installed DEFAULT to 7 MAIN TABS    
 
Figure 2:  MAIN TABS shown all tagged (7 MAIN TABS) to another MAIN TAB
Right mouse on any MAIN TAB  Popup will give you Add Button choice   
Figure 3:  Right Mouse Pop-Up 
Select Add Button
Figure 3 – MAIN TABS now display a New button and a Blank Button  Note: The MORE <  >  scroll
that allows users to view the additional buttons added in the MAIN TABS.
 
The same routines apply to SUB TABS - more details in SUB TABS