Hello Dear,
As I gave your tutorial link, you can change the third image in customizer >> theme options settings >> custom header settings. The third image is for change testimonial background, you can change your image from here.
If above given thing not work, please follow below given steps.
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For testimonial background, you can use given custom CSS in the customizer.
.testimonial-area {
background: url(‘https://fireserviceinternational.com/wp-content/themes/businesso-Pro/images/bg-3.jpg’) no-repeat fixed 0 0 / cover rgba(0, 0, 0, 0) !important;
}
How to use custom CSS: https://youtu.be/5wfcl1t6Pos
How to upload an image and get URL of the image: https://youtu.be/sgjtBOVgDOA
If above given thing not work, please share your username and password with us on our email address [email protected]
We will check issue for you and tell you solution.
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You can contact our skype support team also, just search ASIATHEMES on skype and talk there about your issue.
Thanks and Regards
ASIATHEMES