Hello,
#1. Please copy this code and paste to file functions.php ( child-theme):
function freshio_post_nav(){
$prev_post = get_previous_post();
$next_post = get_next_post();
$args = array();
if( is_a( $next_post , 'WP_Post' ) ){
$args['next_text'] = get_the_post_thumbnail($next_post->ID, array(110, 110)) . '<span class="nav-content"><span class="reader-text">' . esc_html__('NEXT', 'freshio') . ' </span>%title' . '</span> ';
}
if( is_a( $prev_post , 'WP_Post' ) ){
$args['prev_text'] = get_the_post_thumbnail($prev_post->ID, array(110, 110)) . '<span class="nav-content"><span class="reader-text">' . esc_html__('PREV', 'freshio') . ' </span>%title' . '</span> ';
}
the_post_navigation($args);
}
#2. Ok, I updated your account, please recheck.