Hi Stephanie.
Per our Scope of Support / Terms, we do not provide support for non-default WordPress themes (like Twenty Sixteen).
Also, our plugin’s default post types are Events, Organizers, and Venues. Maybe your theme renames Venues to “Places”?
Specific to your question, though, the code to register the Organizers custom post type is here: https://github.com/moderntribe/the-events-calendar/blob/4.2.7/src/Tribe/Organizer.php (look for “register_post_type”)
And similarly for Venues: https://github.com/moderntribe/the-events-calendar/blob/4.2.7/src/Tribe/Venue.php
You can also refer to WordPress’ register_post_type() to see mention of how to add a metabox specific to a custom post type.
If I’m understanding the thought behind their response correctly, they would be the ones to add their own metaboxes to one or more custom post types. They could leverage the tribe_events_register_organizer_type_args and/or tribe_events_register_venue_type_args filters to add their metabox code.
I hope this moves your project further along!
Please let me know if you have any follow-up questions on this topic.