upgrade a c++ 11 project to c++ 17 standard and take advantages [closed]

I am working on a big c++ project (c++11). It contains more than 100k lines, I have to upgrade the whole project to c++17. For instance, I just change flags/config and the project compiles well on c++17. Is there any strategy to localise parts of code: Methods/classes... to upgrade and take advantage of c++17 optimizations?