Happy to help. What you are referring to are known as social proof social pop-ups. There are a wide variety of these types of apps available in our app store. Below I've shared a couple of great options worth checking out as well that I think will suit your needs:
If there is anything else I can help you with, please let me know.
You can check out Zotabox 20+ Promotional Sales Tools including Testimonials and Social Review. You can display your Google or Facebook reviews on your website automatically or upload your own reviews. You can customize the look, style, position, color etc of the reviews and choose which pages to display on. You can check out our app here. I hope this information helps you.