On the Disco interface go to the top of the screen and select 'Programming Mode' Button. You Should see the a screen display similar to the one below.

Right Click on the first fixture you would like to set the address to and select ' View Fixture Dip Switch Settings and Start Channel' From the menu options.

The pop up window below will appear showing you the Start channel and the dip switch setting, if applicable, to the fixture selected.

The fixture properties window show the Fixture name, Fixture Number, Fixture Start Channel, and Amount of channels used. For fixtures with dip switch settings that is also displayed.