I am assuming you’ve PHPMYADMIN , not going in detail as to how you install that and all that crap

First identify the attribute id of the is_anchor attribute:

SELECT * FROM eav_attribute where attribute_code = 'is_anchor';

I get attribute 54 as my query not sure what you will get as that’s all depends on your environment

Now let’s run a Query to update all category to Anchor YES

UPDATE catalog_category_entity_int set value = 1 where attribute_id = 54;

TADA !!!!!!