Hello,
“Close first tab by default” you can find in Theme Options > E-commerce > Single product page.
The position of Size guide can be changed only via additional customization. Copy description.php file (xstore/woocommerce/single-product/tabs) into same folder in your child theme and add etheme_size_guide();
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then add this code in child-theme/functions.php
add_action('wp', 'customize_template_hooks', 65);
function customize_template_hooks () {
remove_action( 'woocommerce_single_product_summary', 'etheme_size_guide', 21 );
}
Regards