How to correct standalone AP Invoice Distributions?

Experts,

Here is the situation.

I have created an supplier invoice with one line and three distributions. I have to correct that invoice by the means of CM. I want to apply that CM at invoice's distribution level.

While entering CM I chose Invoice as match option and selected the invoice. But the 'correction' WON'T give me option to apply it to invoice distribution. It can go till invoice lines only. When I apply to line it distributes the credit to all distributions equally.

How can I drill down to distributions level?

I will appreciate if you can describe the process in detail.