Lately, we have some questions about change names in sitemap XML files in WordPress.
For users Yoast SEO and other plugins:
It’s not possible because the plugin creates automatically sitemap files on the existing post type.
In Vehica post type its called vehica_car and XML file is named vehica_car-sitemap.xml
If you are a developer:
On official Yoast GitHub its an example of file how the sitemaps are created. You can use this to create your own sitemap generation system for your website.
WordPress yoast seo plugin, generate custom sitemap for custom URLS · GitHub
We can’t provide a code for you. You do it at your own risk.