It's been awhile for me, but if I remember correctly, a pair of needle nose pliers to carefully grasp the 'squeezable' part, squeeze it just enough to get it in the pin hole and in the groove, and release. Then the other side.. Make very certain you have the rod/piston orientation CORRECT... and if your parts are numbered that you match up piston and rod... Once the spirolock is installed, I like to 'rotate' it in the groove a little to make certain it's seated fully in the groove.
PS. hint... oil slingers go next to the journal, NOT facing the sister rod... (I took apart an LT1 once that some 'fellas' had installed them backwards...