How to display the first interface when clicking again on the plugin instead of the second interface ?

Hello,

I am developing a python plugin on QGIS which has 2 interfaces ( clicking on a button on the first interface opens the second interface). When I close all the interfaces and I open the plugin again, the second interface is displayed and to come back to the first interface I must close the second interface. What I want to do is when clicking again on the plugin, the first interface will be displayed. Any ideas to do that ? Thanks in advance