Here it is

As an example we'll install jekyll and bundle via this method, but you should be able to do this with any package. First we will 'cache' the packages locally on a machine that has internet access.
  1. Create a local installation directory:
    mkdir gem-local
    
    Here I used `gem-local` but you can use whatever name you like.
  2. Install the packages you want, in that directory:
    gem install   --install-dir gem-local
    
  3. Then you want to transport that `gem-local` folder and get it on the offline machine.
    To install from the cach folder, cd in to it and run gem:
    cd gem-local
    gem install --local jekyll bundle
    
That should work for you, good luck!