As you are already running the Rails application in production u need to run
RAILS_ENV=production bundle exec rake assets:precompile
Dont forget to use RAILS_ENV=production. After precompiling Old Assets will be replaced by the new ones
You might also need to edit config/environments/production.rb file and modify as following
config.serve_static_assets = true
config.assets.compress = false
config.assets.compile = true