// Assign the value of the extracted variable from the recorded step 'ExtractedVar' to a variable to use in the code
var extrVariableInCode = GetExtractedValue("ExtractedVar");

// Insert the necessary custom code to modify the exctracted value and assign it to a string variable
string newValue = "newValueToAssign";

// Assign the modified variable to a new extracted variable
SetExtractedValue("ModifiedExtrVariable", newValue);