Creating your own template is very easy. Navigate to any board (or create a new), and when you are happy with it, hit the "Save as template" from the board menu top-left.
NB: To access this feature, you need a Business or Enterprise subscription.
If you want to make changes to that template, you can overwrite it by setting the same name in the "Save as template" dialogue. Choose "Replace" when asked. Renaming or deleting a template can be done from the Workspace -> Templates tab.