Activating processbook

Hi

Its more of a VBA question realated to PI, How can I activate a display of already open processbook. Like in my case, from display of one processbook say abc I am invoking to open a display of another process book say xyz, now when in display xyz user clicks a button, this xyz processbook has to close and I want to activate the already open display of processbook abc. How can it be done?

Would be grateful for the help,