Azure functionapp unable to update container

I'm working with azure cli and I'm deploying a function app with a container - I'm tagging it like so:
`appName:test`
And I call `az functionapp create` to create the app with the specified container.

When I deploy for the first time, it's fine, but when I try to deploy again, the function won't update - how do I make the function download and use the new container I created? The docs don't mention it at all, and I'm not sure if this is a BUG|DOCS|FEATURE...

I did find this: [https://docs.microsoft.com/en-us/cli/azure/functionapp?view=azure-cli-latest#az-functionapp-update](https://docs.microsoft.com/en-us/cli/azure/functionapp?view=azure-cli-latest#az-functionapp-update)
But it's confusing since I have no idea what it's supposed to update, it doesn't seem to do anything.

** `az functionapp config container set` does nothing either.