At this time there is no way to directly Initialize a Pattern. The easiest way is to select an empty Pattern, then save that to the Pattern location you want to initialize.
There is another way to do this, but it's only recommended if you haven't created any User Presets, or if you have them properly backed up. Power on the Command Station while holding down the two Cursor buttons to boot into Diagnostic Mode. Now scroll the data wheel until you get to the option "17 Init Data Except Seq". This will erase all User data (Presets, Multisetups, User Arps, etc) except for any User Songs and Patterns you may have. Make sure you do not select "16 Initialize User Data", as that will wipe out ALL of your User data.