how to change the H1 after viewing the long description – SEO

On my webshop I display a short text (<350 chars). The customer can press read more in order to see the long description of a category or product.
The problem is by doing that i have 2 H1’s in the page, while only one H1 is recommended for SEO.

The text is getting pulled from PrestaShop, where all the blogs are being stored.

This is the code from category.tpl

 {if $category->description}
                            <div class="cat_desc rte">
                            {if Tools::strlen($category->description) > 350}
                                <div id="category_description_short">{$description_short}</div>
                                <div id="category_description_full" class="unvisible">{$category->description}</div>
                                <a href="{$link->getCategoryLink($category->id_category, $category->link_rewrite)|escape:'html':'UTF-8'}" class="lnk_more">{l s='More'}</a>
                            {else}
                                <div>{$category->description}</div>
                            {/if}