If you are talking about the missing covers (instead of just adjusting the cover page for a single page view in a facing (double page) view), you should then use some free pdf editor or pdf reader/tool with a page-merge or page-add capability.
https://pdf.wondershare.com/top-pdf-...kaAty7EALw_wcB
https://www.lifewire.com/best-free-pdf-editors-4147622
Tools:
https://pdfill-free-pdf-tools.en.softonic.com
With PDFill-FREE-PDF-Tools we can use button no.9 (convert images to pdf) and then button no.1 (merge pdf files).
cpdf
https://www.coherentpdf.com/usage-examples.html#6
cpdf -merge in.pdf in2.pdf -o out.pdf
" Merge in.pdf and in2.pdf into one document, writing to out.pdf. "
If you just want to automatically (by default) show the cover as a separate page in a double page (facing) view, it should be possible to accomplish with quite a few free pdf editors/tools, but we can also choose either to see a separate cover (in a facing view) or together with an adjacent page in almost any pdf reader as well.