Generally, while using rbenv, you can set the global ruby version you want to use through
rbenv global [2.4.1]
But that would set the ruby version for whenever a local version is not set. When you invoke
rbenv local [2.4.1]
you set a specific version for the project you are working in (actually it simply creates a .ruby-version file with the version number in it.
My guess would be that Rubymine would also pick that up (I don’t have ruby mine), as I can only expect it to open up an environment that is based on your other settings, but this is something you might want to verify though.
Where to find that? Well, this might get you started: https://www.jetbrains.com/help/ruby/rbenv-support.html