Hello Luis, welcome to the Prismic community forum!
The short answer is: It is not possible
Prismic does not provide site domain customisations. You'll need to use a hosting service to get a custom domain name for your site, like Netlify.
Or if you were wondering about having a Custom domain for de CDN, I should point out that we do not recommend this. We have a more detail explanation about it in this other thread:
Also, a note about the repository name: It is possible to change the name of your repository, but is not possible to change the name of the API endpoint.