Microthemer is a CSS editor, and so only allows you to customize the appearance of content already on the page. So you can’t use it to edit text content. You should be able to use it to re-position the primary menu. However, sometimes it makes more sense to move the actual content rather than use CSS to ‘hack’ things into place. It really depends how far away from the header your menu currently is. If you can send me a link to the page you’re working on I can advise you further.
P.S. Using a page builder like Elementor or Beaver Builder might help with making content changes BTW.