How to change page URL path?

Give this a read, might have a solution for you: https://betterwp.net/wordpress-create-fake-pages/

Otherwise the quickest solution might just be to create an actual testimonials page that is a parent and redirect it to ‘philip-becker’

If you have a page called ‘Testimonials’ then:

Go to edit on your philip-becker page
Choose ‘testimonials’ as the parent under ‘page’ attributes’ on the right hand side when editing.

If you don’t have a ‘testimonials’ page then I’m not sure how you would do that.

Someone else might.

You can try this

Do as Monalicia said, create and empty testimonials page, use it as parent for philip-becker, then install a 301-redirect plugin and redirect https://www.juantutors.com/testimonials/ to https://www.juantutors.com/