Did you see the screenshot? I’m on iPhone 6 with iOS 9.1.
We will check it again…
What I meant was how do I add the pictures for the testimonial slider. You told me to do that with featured image. But how can I add more than one picture there?
Please go to WordPress admin -> Appearance -> Testimonials and create the testimonials there, please set for each entry a featured image! For the testimonials (also portfolio, team, …) it’s like for the blog: you need your entries and then you can show it on a summary page or with shortcodes.