Simple! Needle nose pliers and pull. Also, I would take off the brass ring that surround the SD. I'm not sure why they have it there but my guess was to create a shadow and make it look like a LD.
FYI The 990/901 and 993 share the same cap, circut topolgy and components. They are identical mics. However, the 990 is side address, or course. So you can skip paying any extra for the 603's and go directly to the 990/991 for usually half the price of 603's.
Look for Frank Vagnola and Bucky Pizerelli CD to be release soon. On that session I used the 991 as ORTF, and the 990 as spaced Omni along with the other tracks in the multi track mix. I think you will like what you hear.
Ray