How do I check if there is a tag in the title

Put this in your loop:

<?php
$title = get_the_title();
$posttags = get_the_tags();

if( $title && $posttags ) {
  $result = find_tag_in_title( $title, $posttags );
  var_dump( $result ); // dump result
}
?>

Put this in your functions.php file:

<?php
function find_tag_in_title( $title, $posttags ) {

  foreach( $posttags as $tag ){
    if( strpos( strtolower($title), strtolower($tag->name) ) !== false ) return $tag->name;
  }

return false;    
}
?>