Load field group for default variation values

I will look into it, meanwhite put the following snippet on your active theme’s functions.php

add_action('woocommerce_after_variations_table', 'trigger_change_event_snippet');
function trigger_change_event_snippet() { ?>

	<script type="text/javascript">
		jQuery(document).ready(function() {			
			$("table.variations select:first-child").trigger("change");
		});
	</script>

	<?php
}

@sarkware thanks for your quick reaction!
I have added this snippet, but there is no changes on the product page yet:

Sorry, I made a mistake in the snippet, here is the updated one.

add_action('woocommerce_after_variations_table', 'trigger_change_event_snippet');
function trigger_change_event_snippet() { ?>

	<script type="text/javascript">
		jQuery(document).ready(function() {			
			jQuery("table.variations select:first-child").trigger("change");
		});
	</script>

	<?php
}

@sarkware thank you, Sark! I reuploaded the snippet, but nothing changed. If I open that page with pre-selected variations – field group still isn’t loading.

I think it triggering the change event way too early. we can add a time out like the below. It may solve the issue.

add_action('woocommerce_after_variations_table', 'trigger_change_event_snippet');
function trigger_change_event_snippet() { ?>

	<script type="text/javascript">
		jQuery(document).ready(function() {			
			setTimeout(function() {
				jQuery("table.variations select:first-child").trigger("change");
			}, 800);			
		});
	</script>

	<?php
}

This one worked well! Even 400ms is OK!
Thank you a lot!