[Plugin: Render custom archive] use post instead of archive

Hello, I’m having a little problem…
I made some shortcodes, that are already functionnals, for a plugin, and that plugin provides a new post type. I would like to use, as the index of that post type, another post with one of those short codes, rendered into theme’s “single-page” template. But I can’t find how to override default wordpress behavior and render my choosen post in place of archive page.

Thank you for your help