How to set WordPress timezone in functions.php?

I'm making an ACF options page and trying to add a timezone setting there, so I don't need to expose the actual WordPress settings page to user. I've been trying to find a function to change the global WP timezone setting, but I haven't been able to find one. Anyone have any ideas how to set that? I'm basically trying to achieve the same UIX as the standard WP settings page has for timezone setting, but outside of that page and in my own options page.

Thanks!