Hello,
Thank you for contacting Rank Math and bringing your concern to our attention.
You may refer to our guide here on adding the service schema on your site:
https://rankmath.com/kb/service-schema/
Also, if you have a Google Business profile page with ratings and reviews already, and they are linked to your website, the reviews will eventually show together within your website on the search results pages.
It’s not that you can’t add the star ratings based on the GMB reviews you have on your profile, but that goes against Google guidelines, and as such, it’s not recommended to do so because you could incur a manual penalty.
Google guidelines also state that the reviews should be generated from users only:

You can refer to these guidelines for more information:
https://developers.google.com/search/docs/advanced/structured-data/review-snippet#technical-guidelines
https://developers.google.com/search/blog/2019/09/making-review-rich-results-more-helpful#self-serving-reviews-arent-allowed-for-localbusiness-and-organization
Looking forward to helping you.
Hello,
Since we did not hear back from you for 15 days, we are assuming that you found the solution. We are closing this support ticket.
If you still need assistance or any other help, please feel free to open a new support ticket, and we will be more than happy to assist.
Thank you.