How can I change an answer because I am doing this myself, and checked the wrong box for myself and my spouse, but I have no intro tab to change

Thank you for your question.

If you have started a joint return and wish to file separately, you can do so by starting a new return.

This link contains the steps to start a new return: https://turbotax.community.intuit.ca/questions/1190053-start-a-new-return