Quick question with htaccess redirect code

Hello,

I just switched the main site of my multisite.
So I have redirect all urls of that subsite to the main site.
I want to redirect thousands of posts, pages and taxonomies of example.com/subsite-1/ to example.com

I found this redirect code but no idea on how transform it to my needs:

<If "%{HTTP_HOST} == 'ipstenu.org' ">
	RedirectMatch ^/blog/([0-9]{4})/([0-9]{2})/(.*) https://ipstenu.org/$1/$3
	RedirectMatch ^/blog/(.*) https://ipstenu.org/$1
</If>

(That code involves subdomain. But I only want to redirect an old subsite into the main)

Please help.