About h1 heading

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I am unable to add h1, h2 headings to my site established with Blogger. Although there are options for larger titles in Blogger such as "en büyük" (largest) and "büyük" (large), the h1 tag does not appear when the article is converted to HTML. I am trying to write it, but I am not sure if it is working. How can I add the h1 tag to my Blogger site?