Loading all sublevels while Loading Screen is spinning!

Greetings to all Epic Games and Unreal Engine users, I recently decide to use Kite demo map for a personal open world project and all went good. I’ve started to modify the map, I’ve added collisions, I’ve added the ThirdPerson mode and other scripts but when I’ve made the Main Menu and Loading screen I couldn’t figure out a way to load all sublevels of the map (GDC_Lanscape01) while the Loading screen was spinning. That caused falling down under the map of the character because the surfaces wasn’t fully loaded. If someone know a way to implement this script please synthesized it in a tutorial or a screenshot of the script. I would highly appreciate if you could help me. Thank you in advance and to all members of the community I wish all the best.