How to put a Webflow site under another Webflow site as a sub-directory?

I have two websites hosting on Webflow. This is the current setting:

I would like to put the blog under the main website as a sub-directory.
The result:

Just like what Webflow does:
https:// webflow .com
https:// webflow .com/blog

Does anyone know how to do it? Thanks a lot.