If you have already been using numbered orders and wish to continue in the same sequence, double-click on the "No:" label (just left of the WO number field). Doing this will temporarily unlock the field so that you can type in a starting number other than "000001". Make sure you type in a six-place number including leading zeros.
Save the order, and confirm that it shows up in the saved orders list at the bottom of the screen.
From here on out your WO numbers will go up from the starting number, in line with your old system.
DO NOT use this feature regularly! It is only intended to be used ONCE, ideally when you first start using the system. Using it on a regular basis will result in data corruption.