I guess, I have the same problem.
currently we have a new instance, with a new domain associated and an old instance with an old domain.
Right now, I want to redirect visitors from visiting the old domain when they type for example "domain1.com" to our new domain which is for example domain2.com . However I don't have any idea how to do this correctly or if it is possible. if you have any documentation on how to do this, can you please share me a link? Please help.
(UPDATE): I already solved the problem by reading here. Thank you