How to add custom coded web pages to my Yoast sitemap?

So I am working on a few single-page web apps and will upload them on my DGO host. I want to use the same domain as my Wordpress blog like if my blog is wordpress.org then my web app will be added as wordpress.org/app1, wordpress.org/app2. The question is how to add those URLs to the Yoast sitemap?

You can use any 3rd Party sitemap generator to create the sitemap XML file. Download the file and upload it to your root directory. Submit the URL to Google Search Console.

You can keep seperate property in the Search Console as well seperate Sitemap for it generated by any online tool.