oracle - close form A when open form B -

i use

open_from('b');  

in when-button-pressed trigger open form b form a.
how close form a when open form b using when-button-pressed in oracle form builder?

try this:

close_form('a'); open_form('b'); 

or

call_form('b'); 

by using call_form hide form , display b , when user exit b active.