How to update existing UML model from updated C++ code

We have a UML model that was reverse engineered from C++ code almost 2 years ago by one of our developers. The code does not change very often, but now we have some new class members that have been added to some of our C++ classes. The class members were added in the code, but not in the model yet. We would like to be able to automatically reverse engineer the new class members into the model from a clean code repo. I tried to use the reverse C++ feature, but it created a duplicate class in the model. How can I get it to recognize that the class already exists in the model and needs to be updated instead of completely duplicated?