This is a paid asset, but now you can download Terrain Adjust for FREE, Please keep in mind this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
Detail this asset from Unity Store: Original Link
Terrain Adjust v1.1.1
“If possible, please buy the package to support the developer”
This tool helps you adjust terrain height data to 3D objects.
Sometimes during environment design, this brush can come in handy to adjust the height of the terrain to the elements. The brush sampling position and angle from colliders when you dragging on it. This tool is a lightweight package that won’t mess up your project.
Useful for blending roads / rocks to the terrain, or create ramps.
Adjust terrain height and slope
Customizable brush size / falloff / spacing / etc.
Works as continuous brush
Different blending types
Undo / Redo support
This package does NOT include the sample assets shown in the screenshots.
Need Collider on target object
Works only in editor