Reimport standard meshes in Unity?

Simple question here, how do I reimport the default meshes that comes along with Unity?

I was playing around with shardmesh, and I accidently altered the plane in my assets, the one that comes along with Unity. I can’t seem to figure out how to reimport this, and most sources is about how to reimport FBX files and such.

I know there is the option of reinstalling, but I find this rather drastic. I really need to reimport this mesh, because many different gameobjects depends on it.

Okay, I managed to resolve it by simply re installing Unity. Though I am still interested in a better answer. I’ll leave this question open for some time then.