Bugsy,
My new R9S just arrived, and it includes an extra sheet in the owner's manual.
"Using a pair of channel-lock pliers, grab the recoil system by the front end cap and by the base of the small collar, which is where the outer recoil spring's finished end rests, and carefully compress the spring. Then insert the complete recoil system into the barrel / slide assembly as shown, releasing the pliers. The slide assembly is now ready to be put back into the frame."
Hope this helps.
Bill