The section immediately following "Statement of Purpose/Personal History and Diversity Statement" is "Future Interests or Goals" section. You will want to enter your submission there. If you are on the "Statement of Purpose/Personal History and Diversity Statement", click "save and continue" to move forward to "Future Interests or Goals".
You are able to jump around the application. Avoid clicking "Submit" until you review every section and make sure you are comfortable and confident on your answers. I'd recommend making a checklist from the attached document and place a checkbox next to each one to make certain you have completed it.
Hope this helps.