Release's Just-In-Time File Mounts are subset of Kubernetes Config Map and allow you to add in special configuration files or scripts to any container as it starts running, just before it deploys. The official documentation can be found here. You can add Just-In-Time File Mounts to your Application by going to the App Settings in the sidebar and scrolling down to Advanced Settings.
A Just-In-Time File Mount has three required elements and one optional element
The file to upload
The location to the mount the file in your containers
The containers to mount in the file in
Whether or not the file should be maintained as a secret
Once uploaded, a File Mount cannot be edited; if changes need to be made, delete the file and upload a new one. You can review the data in the File Mount if it has not been marked as a secret.
If the File Mount has been marked as a secret, the View button will be disabled.