System pages - SEO

Hello!
Could you advise how to enable SEO Index: no index/no follow for all system pages? "Checkout page" and "Thank you page" were indexed by Yandex Webmaster and now he said that the "description" for these pages is not filled.
How can I tune it? Is there any chance to enable no index/no follow on the website?
Or do I need to add these links in robots.txt?

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