What chapter do I go about on getting out of the Army for being pregnant, and how do I start the process?

All you have to do is 1. Ensure that you are via tests. 2. Inform your Chain of Command.

Look into AR 635-200 Chapter 8 (enlisted women-pregnancy) and alittle in Chapter 6 (dependency or hardship.)
Primarily chapter 8 talks about the steps required and whats needed to be chaptered for pregnancy. https://armypubs.army.mil/epubs/DR_pubs/DR_a/pdf/web/AR635-200_Web_FINAL_18JAN2017.pdf