Can you post a picture? I haven’t seen this. Is it rubbery or solid feeling?
My first thoughts are using a glowing red stainless dental pick. You can ask just about any dentist for old tools. They usually give them away free. Heat it up and it will usually slice through like butter. I use this technique to remove rock hard Norland optical glue. You could also use a arts & crafts razor knife. Get it red hot and it will do the trick. I wear a inexpensive respirator for melting silicon, it stinks when melting.
Not sure how to tell you to clean up the residual mess unless we can see how delicate or how much you need to remove.
So basically, I am not sure my technique will work. Also, you could try nail polish remover. Put it on a qtip and let it stand on the silicon. See if it will break it down?
I have used WD40 to break down glues too. Once again not sure about silicon.
Hope some of that helps you a little or spurs some thoughts.