Members help other members with technical questions and problems using Writing.Com!
Sometimes reviewers and commenters suggest things that are not possible due to membership levels they didn't pay attention to or a mistaken assumption about what a bold handle means. Mostly, consulting the information in "Writing.Com 101" will settle such questions. Its TOC contains its own search bar.
In this case, while covers are an Upgraded+ feature, there is one option of that feature available to everyone. See Covers from Writing.Com 101 and note the text highlighted in red flagging the applicable sections.
However, if they were suggesting putting an image within the item itself as a illustration, that feature is limited to Upgraded+ memberships for embedding an image, and Premium+ memberships for embedding a photo.
Hope that helps.