Splunk Machine Learning Toolkit: How do you replace a value of one field with the value of another?

I checked the past questions and answers, but I was not able to find a way to do this. Basically the value field of the event is "DERIVE". I need to replace "DERIVE" with the value in Count. I am trying to use Machine Learning Toolkit (MLTK) and I keep getting this error: "Error while fitting "LinearRegression" model: could not convert string to float: DERIVE" This was CSV data uploaded. Thanks for the help.