When creating the formats the new format will look like the latest edited format. Therefore, you might need a format based on an existing and done format.
To make it easier for you you can duplicate the design of a format to a new format:
Open up "Formats" in the left menu
Choose the format you want to duplicate
Type in the new format in width and height
Click on the small arrow next to "Create new format" and click "Create from selected format".
Happy building 👏