Defining Meta Tags with keywords

I want to define "keywords" meta tag. If i use :
<?meta name="keywords" content="key1,key2,..."?>
in generated html file there is two "keyword" meta tag, first is "<meta name="keywords" content="ZK App"/>"
and the second is "<meta name="keywords" content="key1,key2,..."/>".
Owerwriting the first meta tag needed, because robots take the first one.