You should be able to just make this in blender without a tutorial… Look at the shape of it, recreated it as a plane, extrude it to the length of the wall and you are done. In general you would want to make this a part of your wall mesh as well for when you export it to Unreal.
Unreal is not a modeling tool, any type of modeling you do should in 9/10 cases be done in Blender/Maya/3dsMax etc.