If you want to create a new format you can do it here by here
After that you’ll need to give it a name and a format type, if the format type you need isn't here, go to the section on how to create a format type.
If you want to use a different format type that there is available, the is the option to create a new one at the top of the page, you will need to have developer some custom assembler and/or disassembler for this to work.