Hi @dannyyang,
I hope you are well today and thank you for your question.
Sparkling theme is built on a skeleton underscores theme provided by WordPress.org developers, and they had that tag set to be an h1 – it has something to do with screen readers for when blind users use your website.
I have still notified the theme developer about it so that it will be changed in the future version of theme.
In the meanwhile you can try changing this to h6 tag by using the custom child theme of Sparkling theme that is shared in the following topic.
https://colorlibsupport.com/t/multiple-h1-headings/#post-62628
Best Regards,
Movin