How to add some tag to All site posts?

I don’t believe you can auto add tags, but you might be able to find a plug-in. https://www.ads-software.com/plugins/

that’s easy.
I told, I want to add some tags to all of my site posts (last and new by automatic)

is it possible?

I guess you could loop through all of your posts and use the ‘wp_set_post_tags’ function https://codex.www.ads-software.com/Function_Reference/wp_set_post_tags

Sorry
I update this topic after some months.
Is right now any way or plugin to do this work?
thanks