If you need to remove the shutter for whatever reason , either to perform a CLA on the shutter, or to attend to problems with the focus mechanism, the first obstacle you run up against is the retaining ring. When I worked at Kodak there were always spanners to do this job ready to hand, but you will need to find your own solution.
In many of the Retina I models you can access the retaining ring fairly easily with a traditional spanner wrench, but with the Retina II models the rear lens group sits high, and the very thin retaining ring is deep in the gap between the mount and the lens. This handy tool made by Beljan Manufacturing makes short work of the difficult task of dealing with the retaining ring.
Here is a photo of a shutter I have removed from the camera to show clearly how the tool engages with the notches in the retaining ring.
This tool is currently my weapon of choice when dealing with any of the Retina I or Retina II models, also the Retina Ia & IIa.
You can contact the manufacturer directly by email at beljanebay@gmail.com or do a search for "Retina Agfa Ansco Zeiss Lens / Shutter Wrench" on Ebay.