Missing required field « updated »

http://www.google.com/webmasters/tools/richsnippets gives a list of errors

Missing required field « updated »

According to http://blog.jsansonnens.ch/post/wordpress-et-loutil-de-test-des-donnees-structurees-de-google/ , the line

<time class=”entry-date” datetime=”%3$s”></time>

should be replaced by

<time class=”entry-date updated” datetime=”%3$s”></time>

somewhere, but I cannot spot it in Customizr. How can I make this change in my Customizr Child ?

Thanks !