[HELP] how to add an external page to the existing wordpress xml sitemap

HI there

My site has the following structure:

1. landing page mysite.com (no CMS, pure HTML)
2. wordpress blog in a subdirectory mysite.com/blog/

I installed the YOAST SEO plugin and generated a sitemap mysite.com/blog/sitemap_index.xml

Now I would like to add my landing page to this sitemap. Have no idea how to do it. Can somebody help me?

nobody knows? How you guys solve the problem with the sitemap if your blog is in a subdirectory?

You can submit multiple sitemaps. Create another one for the static site.