How I can shorten this title length?

Because this is in a plugin, you don’t actually want to directly modify the plugin file itself. If you do that, you won’t ever be able to update the plugin without overwriting your work and needing to find it and add what you did again.

Instead, there’s a filter set up in the plugin for exactly this situation:

// in the plugin file:
function msp_get_template_tag_value( /* variables */ ) {
  // ... other stuff we don't care about
  // line 1037:
  return apply_filters( 'masterslider_get_template_tag_value', $value, $tag_name, $post, $args );
}

Line 1037 is a filter, which means you can modify what the plugin creates and replace it with whatever output you want. To do that, add the following in your functions.php file in your theme:

add_filter('masterslider_get_template_tag_value', 'wpse183153_shorten_master_slider_title', 10, 4);
function wpse183153_shorten_master_slider_title($value, $tag_name, $post, $args){
  if ( 'title' != $tag_name ) {
    return $value;
  }

  $short_title = $value;
  if( strlen($value) > 50) {
    $short_title = explode( "\n", wordwrap( $value, 50));
    $short_title = $short_title[0] . '...';
  }
  return $short_title;
}

This function checks to see if the current tag being edited is the title. If it isn’t, then it just skips and lets the content be what it was. If it is the title, then it checks to see if the value is longer than 50 characters; if it is, then it truncates that value and appends ‘…’.