Please follow these steps to add custom button instead of review curse link :
1. Hide the review course button :
a. Go to WP Admin -> Appearance -> Customise -> Custom CSS
b. Add this CSS :
input.review_course[name="review_course"] {
display: none;
}
.more_course .review_course{margin-top:20px !important;}
2. Now add your custom button by addign the given code in your wp-content/plugins/wplms-customizer/wplms-customizer.php file :
add_action('wplms_course_start_after_timeline','custombuttonnwithcutomlink');
function custombuttonnwithcutomlink(){
echo '<a href="http://www.google.com"><button class="review_course unit_button full button" name="submit_course"></button>'.__('Custom','vibe').'</a>';
}