Certain Brushify Landscape packs come with Alpha Brushes for landscape sculpting. To see if your pack contains an alpha brush, check the product description on Unreal Marketplace.
What are Alpha Brushes? An Alpha Brush is a heightmap that is used for sculpting the landscape. It's used to add detail to the landscape.
Each Brushify alpha brush texture contains 4 Alpha Sculpting Brushes
These are stored in the R G B A channels of the texture. That's why the sculpting brushes have an interesting multi-colored look in the content browser as the preview shows all 4 alphas combined into one image.
First Locate the top bar
Click Activate Landscape Editing Mode
This will open the Landscape side bar on the left. Choose Sculpt
Locate Brush Type and select Alpha Brush