How can I return a rotated plane to its original orientation

Question

I have a plane defined by $3$ points (each point has $X,\, Y,$ and $Z$). The plane has been arbitrarily rotated on its $3$ axes, and the three points have been remeasured -- thus, I know the coordinates of the $3$ points before and after the rotation. I now need to reorient the plane so that it is in its original orientation. If possible, I would like to do this by using the angle differences in the $XY,\, XZ,$ and $YZ$ axes (that would make it easier for me to understand), but most importantly I need a solution that I can use in a VB program or excel. My math skills are minimal, so walking me through it with baby steps would be very much appreciated. Thanks for your help.