Hii, how can I delete the others countries (Germany, UK...)?

If you set your mod to be a "Country Overhaul" mod, by pressing "Edit mod" on your mod's page (where you export it from) this will remove all of the default countries.

If you only want to remove a specific country/set of countries, e.g. just Germany, or just the European nations, you will need to create a new country and assign it all of the states of the countries which you do not want to exist.