Hi Blossy, Your pearls are glorious! This certainly one of those times when a 3rd hand would be nice. I've come up with a way that works for me, and perhaps would for you also.
Drape the bracelet over your arm. Firmly press your wrist with your pearls draped over against the towel on the towel bar. This way the bracelet will hold still will you maneuver the insert over the safety catch, then push into place. For me, it makes it possible, not necessarily easy. I use this for most bracelets with lobsters and the like, except toggles. Let me know if it works for you. BTW, I'm so glad your bracelet and earrings arrived.