Best way to post a sequel

My newest fic had some requests for me to write a different pov in. I never do sequels, so I'm not sure what the best way to do it is. Do I: 1- post a new chapter on the old fic? 2- make it part of a collection. (How do u even do that? I can't find the option) 3-just post it and write that it's part 2 of something else in the summary. Help, please