You’ll want to use the Level Streaming Volume for this. It is a volume created by epic to handle exactly what you’re looking for.
Check out the docs for Level Streaming Volume here:
Hope this helps!
Thanks a lot! another question. Let’s say i want things in a level to change, like maybe new walls come up or walls disappear. How do I do that??
I’d recommend watching the Level Streaming Livestream over on the Unreal Engine Youtube channel, it covers a lot of that stuff.
Also could you please mark answer as correct so it shows as solved 
Suppose I’m on a level, say level 1. Level 1 has a trigger box, once the player steps into the trigger box, another level immediately loads, say level 2. My question is, how do load one from one level to another without a loading screen?
For example, I want the player to enter flashbacks every now and then. How does one do that without adding a loading time??