salar2016 on "how to update post meta when 70 days of published post"

Hi
I want to update automatically specific custom field to new specific value after 70 days from published post . ( i have 6000 posts in my blog )
for example in beginning create post set "level_tutorial" = "advanced"
i want set after 70 days "level_tutorial" to "Beginner"
tanks!
I know a little bit about ( update_post_meta ) but I do not know how to put in this case