This might help you.
After you create a page using the page builder. You have to link to it with your menu system. So in your current case as mentioned. You should disable your current testimonials page link. Then create another link for testimonials that link thru the jdbuilder option in create a link. After you do this when you click on the testimonial link you will see the page that you created. The next step would be to assign whatever modules you want to the page from your old page and so on.
Good coding. Hope this helped.
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