1. Create a new document in CorelDraw.
2. Click on the Polygon Tool in the Toolbox Toolbar
and create a polygon.
3. In the property bar, set the points or sides to 3.
This should make the polygon into a triangle.
4. Right click on the triangle and convert it to curves.
5. Go to Windows >> Dockers >> Fillet/Scallop/Chamfer
In the Fillet/Scallop/Chamfer docker, make sure that Fillet is selected and then click on Apply.
Here is the final result.