In box-message.php see a line <div id="fep-message-<?php echo fep_get_the_id(); ?>" class="fep-table-row">.

If you use HTML5 then add

<a href="<?php echo fep_query_url( 'viewmessage', [
	'fep_id' => fep_get_the_id(),
	'feppage' => isset( $_GET['feppage'] ) ? $_GET['feppage'] : 1,
	'fep-filter' => isset( $_GET['fep-filter'] ) ? $_GET['fep-filter'] : '',
] ); ?>">

before that div and add </a> after closing that div.