Automatically set default meta for new entries

You can use https://codex.www.ads-software.com/Plugin_API/Action_Reference/save_post

So I’m getting it to update the correct meta fields when creating a new entry, but it’s not reading the fields to put in there. Here is my function:

function update_yoast( $post_id ) {
	$focuskw = '_yoast_wpseo_focuskw';
	$title = '_yoast_wpseo_title';
	$metadesc = '_yoast_wpseo_metadesc';
	$jobtitle = get_post_meta( $post_ID, '_job_title', true );
	$city = get_post_meta( $post_ID, 'geolocation_city', true );
	$shortstate = get_post_meta( $post_ID, 'geolocation_state_short', true );
	$longstate = get_post_meta( $post_ID, 'geolocation_state_long', true );

	update_post_meta($post_id, $focuskw, $jobtitle . ' in ' . $city . ', ' . $shortstate . ' - Darts Bar Databases');
	update_post_meta($post_id, $title, 'Find hours, reviews, and info on ' . $jobtitle . ' and the best ' . $city . ', ' . $longstate . ' bars. Discover nearby darts leagues and tournaments.');
	update_post_meta($post_id, $metadesc, $jobtitle . ' in ' . $city . ', ' . $shortstate);

}
add_action( 'save_post', 'update_yoast' );

Is get_post_meta not the correct function to use?

Yes but post_id is case sensitive.