How do I increase the memory limits for a one-off dyno?

Resolution

One off dynos can use any of the available dyno types via the --size argument. You can find instructions for using this here https://devcenter.heroku.com/articles/one-off-dynos#one-off-dyno-type

Please note that the use of larger dyno sizes for one-off dynos requires the web dyno for the app to be at least standard-1x (i.e. not free or hobby). If you are not using web dynos for your app you can set these sizes and then scale the web process down to zero to continue using larger one-off dyno sizes.