Offset texture alpha channel

I would like to scroll the alpha channel for a texture that is using the transparent/diffuse shader.
but I have no idea how to tell SetTextureOffset to acces the aplha channel.

The alpha channel is not separate from the rest of the texture. Do you mean an alpha cutoff (for that, use Transparent Cutout).

If you need to scroll the alpha, you will need to make a new shader. Probably easiest to put the alpha on a whole new image since you’ll need two texture samplers anyway.