From Astra customizer settings ( Customize > Header > Site Identity > Site Tagline / Site Title ), you can add the Title or a Tagline for your site. A Site Title is the name of your side, and the tagline is a small catchy descriptive line for your site.

By default, the Title has Heading 1 tag

while tagline has paragraph tag

in HTML structure. You can change this tag to any other HTML tag using the following filters:

Change Tag For a Tagline

add_filter( 'astra_site_tagline_tag', 'astra_change_site_tagline_tag' );

/* Function to change tag of Site Tagline.
@param string $tag Default is p tag.
*/
function astra_change_site_tagline_tag( $tag ) {
$tag = 'h6';
return $tag;
}

Note:

1. Above filter will change tag to tag. You can update it as per your requirement.2. Paste the above code in the child theme』s functions.php file.

This is how your Default tag looks in your code:

And this is the change from

to

in your code after adding the Filter:

Change Tag For a Site Title

You can also replace the H1 tag for the Title with span tag using the below filter –

add_filter( 'astra_site_title_tag', 'astra_function_change_site_title' );

/**
* Function to replace h1 tag with span in site title.
*
* @param string $tag This contains the tag used for site titles.
* @return string
*/
function astra_function_change_site_title( $tag ) {
$tag = 'span';
return $tag;
}