Create template file
Create a copy of turbo-pages.hbs file and put it inside the folder of your theme.
Update routes rules
Open settings of your ghost blog Labs → Routes, and add next code for the section routes:
routes: /rss/turbo-page/: template: turbo-page.hbs content_type: text/xml
Update your theme and add page https://your_site/rss/turbo-page/ as source of Turbo-pages.