By default the search fields and buttons on a data grid are left aligned. I think you might have changed some CSS for data grid which made it right aligned. Please check your custom styles. As the best practice you should add your custom styles in SASS and compile to CSS using Calypso or Koala etc. instead of changing CSS directly. If someone update SASS and compile it, your changes in CSS will be overwritten.
If required, you can go through Style your App with CSS learning path.
Hope this helps!