Opening a Form from a child from to show on the ManForm Panel

Hi Forexlearn, 

I've been working this project and I have been stuck for 3 days now, hence i need some help. This is my issue. 

I have a MainForm that has two Panels. PrimaryPanelHolder and a PrimaryPanel (tablePanelLayout).  I load a a child form onto the PrimaryPanel then from the child form A, i want to loand another child form B to show on the mainForm inside PrimaryPanelHolder.  My calling from is the  Child Form A. How can i get this one right? I search all the online forums but I didnt come across any solution.