Basic stuff - just open it up, and select Division Designer - not an existing template

The game will show you one of your existing divisions, but just click on the division type option, just above the field regarding the division name choices. There will be a list of all your templates, as well as an option for creating a new one.

By now you should be where you want to be - a fresh template with nothing in it!

And now you can add in that first battalion for just 5 xp!