Call Level Begin Play in C++

Hello,

I have levels like: Login, Loading and MainMenu, I created Widgets for them which contains graphics like background image and so on, they are called WBP_Login, WBP_Loading and WBP_MainMenu.

I wonder how I can set these Widgets to UI when player enters some of these levels in C++, because there is nothing like Level C++ Class afaik which contains Begin Play for specific level.

Thank you