Typically, the amine oxide is prepared from the corresponding amine with a peroxy acid or comparable oxidant. The actual elimination requires just heat.
^Peter C. Astles; Simon V. Mortlock; Eric J. Thomas (1991). "The Cope Elimination, Sulfoxide Elimination and Related Thermal Reactions". Comprehensive Organic Synthesis. Vol. 6. pp. 1011–1039. doi:10.1016/B978-0-08-052349-1.00178-5. ISBN978-0-08-052349-1.