How to using Co-Authors plugin with Zelle

Important notice: This product is now in maintenance mode and is no longer being actively developed or supported. Updates and bug fixes will not be provided unless they relate to security concerns.

To integrate Co-Authors Plus, you’ll want to replace existing author template tags in your theme with a simple conditional that uses the Co-Authors Plus template tags if Co-Authors Plus is available. The conditional prevents your site from breaking (e.g. white screen of death) if Co-Authors Plus isn’t activated.

You need to login to your FTP, and navigate to theme's /inc/ folder, and edit template-tags.php file. Replace the following block of code:

function zerif_posted_on() {
	$time_string = '<time class="entry-date published" itemprop="datePublished" datetime="%1$s">%2$s</time>';
	if ( get_the_time( 'U' ) !== get_the_modified_time( 'U' ) ) {
		$time_string .= '<time class="updated" datetime="%3$s">%4$s</time>';
	}
	$time_string = sprintf( $time_string,
		esc_attr( get_the_date( 'c' ) ),
		esc_html( get_the_date() ),
		esc_attr( get_the_modified_date( 'c' ) ),
		esc_html( get_the_modified_date() )
	);
	printf( __( '<span class="posted-on">Posted on %1$s</span><span class="byline"> by %2$s</span>', 'zerif' ),
		sprintf( '<a href="%1$s" rel="bookmark">%2$s</a>',
			esc_url( get_day_link(get_the_date('Y'), get_the_date('m'), get_the_date('d')) ),
			$time_string
		),
		sprintf( '<span class="author vcard" itemprop="name"><a href="%1$s" class="url fn n author-link" itemscope="itemscope" itemtype="http://schema.org/Person" itemprop="author">%2$s</a></span>',
			esc_url( get_author_posts_url( get_the_author_meta( 'ID' ) ) ),
			esc_html( get_the_author() )
		)
	);
}

And replace it with the following

function zerif_posted_on() {
    if ( function_exists( 'coauthors_posts_links' ) ) :
        printf( __( '<span class="%1$s">Posted on</span> %2$s <span class="meta-sep">by</span> %3$s', 'zerif' ),
            'meta-prep meta-prep-author',
            sprintf( '<a href="%1$s" title="%2$s" rel="bookmark"><span class="entry-date">%3$s</span></a>',
                get_permalink(),
                esc_attr( get_the_time() ),
                get_the_date()
            ),
            coauthors_posts_links( null, null, null, null, false )
        );
    else:
        printf( __( '<span class="%1$s">Posted on</span> %2$s <span class="meta-sep">by</span> %3$s', 'zerif' ),
            'meta-prep meta-prep-author',
            sprintf( '<a href="%1$s" title="%2$s" rel="bookmark"><span class="entry-date">%3$s</span></a>',
                get_permalink(),
                esc_attr( get_the_time() ),
                get_the_date()
            ),
            sprintf( '<span class="author vcard"><a class="url fn n" href="%1$s" title="%2$s">%3$s</a></span>',
                get_author_posts_url( get_the_author_meta( 'ID' ) ),
                esc_attr( sprintf( __( 'View all posts by %s', 'zerif' ), get_the_author() ) ),
                get_the_author()
            )
        );
    endif;
}

That should do. You can visit their official docs for more info.