User submission and approval

Testimonials are a custom content type, and as such, they can only be added through your site’s dashboard, similar to how you would draft a new post. Therefore, they can only be added by the site’s administrator (and editors, authors, contributors) and not by your users.

Instead, you can collect testimonials from your interactions with your customers, and then with their permission, add them to your Testimonials section to share with your site’s viewers.

Here’s more about the Testimonials feature:
https://jetpack.me/support/custom-content-types/