Facebook - how do you link an existing page to a group?

In group settings for Facebook groups, at the end, in the Advanced settings section, there is an option to Link a page, but when I click it, it starts the guide to create a new page. I want to link an existing page. IIRC, you could do that in the "classic page" UI, from the page, not the group, but I can't find that option anymore when I look in my page settings (which doesn't rule out that it exists, everything is just very hard to find these days)