Create new container images on Windows Admin Center
Create new container images
When working with containers, you'll write instructions to Docker on how your container image works, and then Docker creates a new container image based on these instructions. These instructions are saved on a file called "Dockerfile" that's saved to the same folder in which your application resides.
Step 1:
Windows Admin Center can considerably reduce the overhead of writing Dockerfiles or even remove the need to write these files entirely. To get started, on the Containers extension, select the Create New option on the Images tab.

Step 2: Select: Use an existing Dockerfile
Use an existing Dockerfile: This option allows you to rebuild a new container image based on an existing Dockerfile. This is useful when you need to make small changes to an existing Dockerfile or when you need to recreate the container to catch an application update.
Step 3: Enter: Application source path: C:\app
Once you select the type of application you want to containerize, you can select common options to finalize the creation of your image:
Enter:
Application source path: C:\app
Step 4: Click Build
Reference:
https://learn.microsoft.com/en-us/virtualization/windowscontainers/wac-tooling/wac-images