I’m not sure what you mean but maybe it helps if you follow a tutorial about creating a landscape.
If you are new, you will run into more problems.
A course will lay down a good foundation and you will learn more in a shorter time.
I bought this one, at the 2nd game you are going to adjust the landscape.
Personally, I think he is doing a great job.
He gives a good explanation and shows how it should be done.
Definitely worth the money if you are new. https://www.udemy.com/unreale4/
Hopefully this will help you with your problem.