Use below steps to adjust the button size:

In MC open POS Customization-->Layouts-->Select Layout(Edit)-->POS Designer

--In the Customization Window, click on Customization

-- In the customization tree drag the "blank" on the preview, between the "TransactionGrid" and "TabbedControlGroup1" 

-- Right-click on "TransactionGrid" and select "size constraint" > "Lock size"

-- Now select the empty space from the design and drag it back to the "customization window"

-- In the background, you can see the "TabbedControlGroup1" area is extended 

--Click on OK to save the changes

Ticket Reference: #14581