First you have to install the plugin. In the menu at the top, go to View then click on Commands. The commands will appear on the right side (and note that you can just start typing the name of a command to filter it out). Click on this one "Plugins: Show plugin manager". Then on the Plugins, make sure you go to the Available section. Scroll down and find Vim and click on it.

Now you have to enable it. Go back to Commands and find "Settings: User behaviors" . Then go to the :editor section between the square brackets. Type "vim" and it will show a popup with several items it can complete. Pick this one: "Vim: Activate Vim mode". It should then insert this: :lt.plugins.vim/activate-vim Save the file and it should now work!