How do I upload a manga that is not on here yet?

I don't know but you can asked the people running the cite by clicking the flag on the side of the screen and write the question in the report section if that helps

Upload the chapter on imgbox and copy the link to the album. Find the white flag button that’s on the left side of the screen and click “Upload Chapter”, paste the link to the album and mangago should then upload the manga in a while. Good luck (▰˘◡˘▰)

Don’t forget to mention the title and author of the manga before you press report