can't change the URL of my main site with multisite

Hi,

I have built my new website with wordpress multisite. So this is my new website here: https://www.mydomain.com/themestest/ and my current website is https://www.mydomain.com/

I wanted to change the URL for this to become my main Website: https://www.mydomain.com/ and move the other one to another folder.

So I have followed the 3 steps Mika Epstein is talking about here: https://www.ads-software.com/support/topic/multisite-change-root-blog

I have done the 2 first steps which are:

1. Go to Network Dashboard > Sites and edit the site you want to be the main site. Change that to have the URL you want for you main site (so from example.com with a path of /sample/ to one with a path of / )

Make certain you leave ‘Update siteurl and home as well’ checked!

2. Then go to your wp-config.php, look for this line:

define(‘BLOG_ID_CURRENT_SITE’, 1);

Change it to the site ID you want to use as your main site.

but I struggle with the last step:

Go back to your Sites and edit the old main site. Give its path a new name and press save, making sure you keep that checkbox checked.

When I click to modify the old site, I can’t edit the URL
It’s just the “/” in grey and there is no textarea to modify it.

Many Thanks for anyone that could help me.