Landscape mode (x number of actors needs to be rebuilt)

I am new to game development and unreal engine. When opening up a project and selecting landscape mode, after selecting resolution and size, no matter if it is (7x7, 1x1) or large i will get a red message that states “x number of actors need to be rebuilt”.
I understand that there is probably somewhere in the newly created mesh that needs adjustment, but i an unaware of how i can fix this issue. Could I please get some help with this? I love using unreal so far, even if i have only done like 2 things with it so far. Please and thank you.