Google has just updated its Google Apps or G Suite account for free, as of Jan 10, 2020, we are not able to change the primary domain and add secondary for a google app account free, because google has fixed this bug.

However, you can continue to use this account by adding a alias domain, not changing the root domain is a good option, it helps account is absolutely safe.

We will hand over the root domain name (primary domain) to you along with the super administrator account.