You need to Create catalog_product_view.xml in your custom theme to change text of existing tab
app/design/frontend/Vendor/theme/Magento_Catalog/layout/catalog_product_view.xml
<?xml version="1.0"?>
<page layout="1column" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<body>
<referenceBlock name="product.info.details">
<block class="Magento\Catalog\Block\Product\View\Attributes" name="product.attributes" as="additional" template="product/view/attributes.phtml" group="detailed_info">
<arguments>
<argument translate="true" name="title" xsi:type="string">Change More Information</argument>
</arguments>
</block>
</referenceBlock>
</body>
</page>
If you want to change content of tab you need to change template
<block class="Magento\Catalog\Block\Product\View\Attributes" name="product.attributes" as="additional" template="Magento_Catalog::product/view/attributes.phtml" group="detailed_info">
and create attributes.phtml at
app/design/frontend/Vendor/theme/Magento_Catalog/templates/product/view/attributes.phtml
vendor/magento/module-catalog/view/frontend/layout/catalog_product_view.xml