Are you ask how to submit course completion forms for OCMJD or registering for the assignment/essay or both?
Course completion form:
Contact Oracle customer support through CertView verifying the course you have done fulfills OCMJD training requirement.
Registering for assignment/essay:
Should be the same as registering any exam through Pearson VUE. For the assignment, once registered, Oracle should send you an email how to download the files. Since I have done my JD cert in the Sun days so the actual steps may differ. If in doubt ask Oracle CS
Remember the entire JD process must be done in 6-month period (assignment+essay) from the day you download the assignment.
You already must be SCJP or OCPJP certified. It doesn't matter which versions (1.4, 5.0, 6 or 7). But you must be a certified java programmer. If you are not, you first have to take another certification: OCPJP6 (1 exam) or OCAJP7+OCPJP7 (2 exams: 1 entry-level + 1 advanaced).