Thanks you @Simon_Manning ! Your reply helped and guided us finding a similar way for 2b.
This is what we are going to do for 2b (in case anyone is interested in). After entering rails console:
UserOption.update_all(homepage_id: 4)
homepage_id 4 is “New” in our testing site. I am not sure if it is consistent due to different site settings. But it is easy to check. Just have one user with the default home page set for “New” and get into database to check the homepage_id of this user. The friendly instructions on how to get into database and check data can be found here.