Exclude 1 blog from multi-blog site in XML feed?

I tried to add a second blog to my site. The first issue I came across is setting custom blog.sources on the second blog. My first blog had a directory and {year}-{month}-{day}-{title}.html for blog.sources. When I tried to add another directory + {year}-{month}-{day}-{title}.html for the 2nd blog, the build keeps erroring out. It works with just directory + {title}.html though.

When I checked the existing XML feed if it’s still working, it says:
You have more than one blog so you must either use the flag --blog (ex. --blog 'myBlog') when calling this method, or add blog: [blog_name] to your page's frontmatter

First, I don’t really get what’s it’s trying to tell me to do (where do I put the flag?), second, I only want to include the first blog in the feed, not the new second one. How can we exclude a blog in the feed?

Figured it out. Added to feed.xml.builder.