How to credit Editorial Use images

Hi, I'm writing a nonfiction book, which will include a couple of editorial use only images. 

The guide says "All uses must include the credit line shown on the site and contained in the IPTC credit line field of the file, for example “Agency Name/Contributor Name – stock.adobe.com”.

I am not tech savvy- there is no 'credit line' listed when I look at my download history- I just see the asset ID and the author's name. 
I can't find a "credit line" in an "IPTC" field. Lines about metadata make no sense to me. How do I correctly credit an image that is for editorial use only? 

Thankyou in advance for any help.