Can you modify this to work for your data?

In[1]:= data = Table[{x, x^2 + RandomReal[{-2, 2}]}, {x, -4, 4}] (*make up some data points*)

Out[1]= {{-4, 17.4655}, {-3, 9.35509}, {-2, 2.49318}, {-1, -0.0807469},

{0, -0.417158}, {1, -0.0704794}, {2, 2.71172}, {3, 9.31136}, {4, 15.9621}}

In[2]:= parabola = Fit[data, {1, x, x^2}, x] (*fit a parabola to the data*)

Out[2]= -1.17073 - 0.0949574 x + 1.12112 x^2

In[3]:= Show[ListPlot[data], Plot[parabola, {x, -4, 4}]] (*overlay the parabola and the points to check*)

Out[3]= ...plot to see if it worked snipped...