I don't know if Axiom does anything more, but you can do it by just grabbing a 6-60 second clip of the start of the song you want to continue, and uploading it to the Suno website under the "Create" -> "Upload Audio" option, then clicking "Extend" next to the upload to continue it. Careful, though; using other people's songs as an uploaded clip is technically against their Terms of Service, so they could terminate your account for doing it.
