I have plelnty of experience with C++, I have programmed modules for different projects in C and C++
I'm going to be honest, I don't have as much experience with Matlab and C++, but I am confident enough on my C++ knowledge and skills that I think I can deliver, specially given that you say it's the C++ skills of the other freelancer that are lacking, and not his matlab skills
I believe you can contact me on the freelancer platform without commiting to assigning me the project, and we could discuss the project further