I am working with drupal8. I want to prioritise the h,h2 nd h3 tags when checking view source for SEO purpose.I have "Main navigation" before h1 tag.Either i want to remove the below html or hide from the view source.Is it possible for me to solve this issue?
Page structure is controlled by the theme you're using. It is possible to structure your HTML so that navigation comes after content in HTML source, even though it may appear to be visually "above" content (with the use of CSS).
You may want to change your templates and CSS to reorganize the order of things in your HTML, or use a theme that already does this out of the box.
You can completely remove the Block titles by entering
<none> in the Block title configuration.
You can also change your theme output so Blocks don't use headings as their titles, although it's not clear how important that is for SEO.
There have been indications that if you have your main content properly structured with headings, having navigation before the content in HTML won't have negative consequences.
Related: Should block titles be <h2>?