Try using NMinimize:

http://reference.wolfram.com/language/ref/NMinimize.html

Or try using the FindMinimum function:

http://reference.wolfram.com/language/ref/FindMinimum.html

The first step is to define the function you're trying to minimize. From the context above I can't tell, but it's probably something like

Integrate[(f[parameters]-curve)^2, {x,a,b},{y,a,b},{z,a,b}]

Where "f" is the curve with your parameters and "curve" is the curve you're trying to get it close to.

Notice that "f" and "curve" are 3-vectors. You need them to be a scalar quantity. When you minimize something, you minimize a scalar value. You could chose for example to minimize the magnitude of the vector. That is a common choice.