Need help with iBooks compile

Apple kicked back my epub because the jpg was too large. My cover designer gave me an itmsp file which I dragged into the Scriv project.

When I try to re-compile, Scriv does not see the itmsp file although I can see it in the binder.

How do I delete the existing jpg & replace it with the itmsp file?

Thanks.

Aren’t itmsp files special iTunes binaries for uploading products to iTunes? Do they work for individual images?
Genuine query because I’ve never sent anything to iTunes - my “knowledge” is based on casual reading not personal experience.

Into testing the borders of the truth are we?

Always. Aren’t you?
But that’s avoiding the question Mr IT man, what are “itmsp” files?
And any helpful advice for young Mr/Mrs/Miss/Mstr/Dr/Rev/Prof ecrivain?