如何在嵌入式容器之间从一个嵌入式视图切换到另一个嵌入式视图？

I have two embedded container overlapping in the same place in one view controller. I made them interchangeable by set the hidden property on the container and use a segment control to set the hidden state of the two embedded container, which I have already made it. What I want now is that how can I show the other embedded container when I toggled a button in one embedded container view. The two embedded views belonged to two different view controller class. I tried to set the hidden property when the button on one embedded view is toggled which is set in the parent class to false, it says "fatal error: unexpectedly found nil while unwrapping an Optional value", it means I didn't initialize the "ChangePersonalInfo" which is the embedded container though the parent view controller is created, so how can I initialize it in order to set the hidden property. here is my code I have two embedded container overlapping in th