It depends of the theme you are using. For es-theme-next-level for example, I have to create a folder into share/themes/es-theme-next-level/<NEW DYNAMIC CUSTOM COLLECTION> and inside that folder edit the images logo.png and fond.png
Checl it out how your theme works, and make sure that theme new folder matches the dynamic title text, it’s Case Sensitive.
“X-Men” is different for “x-men”.