Hello there. I have problems because of my impatience and arrogance. 
After successfully creating several multisites on new WP installations I decided to turn an already existing Wp site into multisite. And of course I didn’t really read carefully the documentation especially the one saying that I should be careful whether my site uses www. So, of course it messed up. Now:
1) my new site which is supposed to be the new English language version of the site is not working at all, and
2) when loading my main site it redirects to Error 404 page so I have to click on the Home link in the menu to reach the homepage.
I read the “Before you create a network: Be aware” documentation after I created the network, of course, and I see that it says “If you plan on changing them to domain.com or www.domain.com, do so before you begin the rest of the setup for multisite, as changing the domain name after the fact is more complicated”. But I don’t know where to look for instructions or documentation on how to change it after the fact. I guess that changing it will fix both my problems from above.
Show some mercy to the poor negligent one here!