Will clear out all the specified completed scheduled actions, 5000 at a time.

functions.php

<?php // do not copy this line
/**
 * Will clear out all the specified completed scheduled actions, 5000 at a time.
 */
function clear_woocommerce_scheduled_actions_20200609() {
	global $wpdb;

	$limit         = 5000;
	$actions_table = $wpdb->prefix . 'actionscheduler_actions';
	$logs_table    = $wpdb->prefix . 'actionscheduler_logs';
	$actions_query = sprintf(
		"
		SELECT	action_id
		FROM	%s
		WHERE	status = 'complete'
		LIMIT	%s
		",
		$actions_table,
		$limit
	);
	$action_ids      = $wpdb->get_col( $actions_query );
	$ids             = implode( ',', array_map( 'absint', $action_ids ) );

	if ( ! empty( $ids ) ) {
		$deleted_logs    = $wpdb->query( "DELETE FROM $logs_table WHERE action_id IN ($ids)" );
		$deleted_actions = $wpdb->query( "DELETE FROM $actions_table WHERE action_id IN ($ids)" );
	}

}
add_action( 'action_scheduler_run_queue', 'clear_woocommerce_scheduled_actions_20200609', 999 );