Firstly it's worth noting that the Submit Button won't appear in the form body of the editor, although you can see what it looks like and edit it in Theme → UI Elements. On the live form, however, the Submit button will be visible.

By default, the Submit Button will always appear immediately after the last visible question on the form. If you would like to move it further down to appear after text or content that comes after the last question, then you can add a question where you would like the Submit Button to appear, and make it a "Hidden" question. The respondent will never see this question, but it will force the Submit Button to be displayed further along.

Note that if the last question on the form is hidden by conditional logic, or are on a page or section that is not included by conditional logic, the submit button will appear on the next, last visible question.