Within that drop down should be the Add or Remove Buttons
option. Click it and then Customize
to jump to the UI for editing the toolbar. Then scroll down to the button(s) you want to move and select it. Then use the Move Up\Down
to reorder the buttons to whatever layout you want.
Note that VS can, with any update, change the layout or contents of builtin toolbars. Therefore I'd recommend that you create your own custom toolbar(s) with what you want on them. Then hide the original/unedited toolbar.
To ensure this doesn't happen in the future export your options using Tools\Import and Export Settings
. Export whatever settings you don't want to customize in the future but specifically you'll want to export the customizations under General Settings\Menu and Command Bar Customizations
. Now, if the bars ever get messed up in the future you can import your settings (or the subset of settings you want to restore).