Right, for AMCAS, any GPA calculator (or a regular calculator, for that matter) can do it. If you got a C and an A-, you would just enter each of those as separate classes (or 2.00 and 3.67 grade points, respectively). So your GPA with only this class and the retake would be the average, 2.835.
If we use DO rules, then you'll just use the higher grade and ignore the lower, so your cumulative for the class and the retake would be 3.67.