I hope i can help you as your theme provider said, you have to create a child-theme and in the template you should remove the author’s reference.
Line 86-89, remove this:
$byline = sprintf(
'%s',
'<span class="author vcard"><a class="url fn n" href="' . esc_url( get_author_posts_url( get_the_author_meta( 'ID' ) ) ) . '">' . esc_html( get_the_author() ) . '</a></span>'
);
(by doing this you are removing the author info)
Line 91 (86 after removing lines 86-89), remove this:
<span class="byline"> ' . $byline . '</span>
(by doing this you are removing the author info call and its container)
This should be the answer to your problem.