In TCPDF there is tcpdf_iclude.php and if you open that file you can see something as
$tcpdf_include_dirs = array(realpath('../tcpdf.php'),
'/usr/share/tcpdf/tcpdf.php',
'/usr/share/php-tcpdf/tcpdf.php', '/var/www/tcpdf/tcpdf.php',
'/var/www/html/tcpdf/tcpdf.php',
'/usr/local/apache2/htdocs/tcpdf/tcpdf.php');
Now check where is your TCPDF folder then add the path in that config file and it will solve the issue. if its inside /home/content/06/11735806/html/systems/CA
then add the following on the include dirs as
/home/content/06/11735806/html/systems/CA/tcpdf/tcpdf.php