Do you mean you want to remove 'Global Search' from the 'Unified Toolbar' ? If yes: Right click on the 'Unified Toolbar ' and select 'Customise' Left click and hold down to grab the 'Global Search' then Drag the 'Global Search' from the toolbar and drop in the section called 'Available for all spaces'

Please note - if you are trying to get the 'Unified toolbar' to look similar to the old 'Mail toolbar' Then I suggest you drag and drop 'Get Messages' and 'Write' onto the Unified Toolbar, plus any other you may desire like 'Tags'. Then click on 'Save' This means you can now hide the new 'Folder Pane Header' toolbar which has that big blue 'New Message' button. Click on the 3 dot icon and select 'Hide Folder Pane Header'.