Reverse U and V with the VB's function : OnSurface.Reverse

Hello!
I am trying to reverse the U and V coordinates of a surface with grasshopper, but it's not possible.
So i'm trying to do it with VB script in Grasshopper but i am not very good with the script.

Is some one could help me?

There is the function : "OnSurface.Reverse(Dir As Int) As Bool
If Dir=0 it's "s" if Dir=1 it's "t"
i don't know what "s" and "t" mean, and i don't know how to write the code !!!