How to find the name of a reference plane used in a mate - API?

Hi,

I am trying to adjust the value of angle mate using an add-in. I developed an add-in that can search the assembly for angle mate and I selected it. But to edit the mate, I need to select the mate entities (in this case reference planes), but I don't know how to select the planes. I hope someone can help me with this.

Thanks.

PS: I am new to SolidWorks API, so don't make it too complicated.

SolidworksApi/macros