I've been in exactly the same situation (I assume your film case is made of thin sheet metal). Being just an amateur, I had no darkroom so I did this at night with heavy curtains in my window, lights off except for a little flashlight covered with some red cloth, so i just could barely see what I was doing.
The point is, slightly opening the film case precisely where the film comes out, I used a non-sharp knife (the kind used for eating, not for cooking), then spin the spindle back and forth. Listen carefully to know when the film lead passes the opening (it makes a subtle clicking noise when you spin it in the winding direction), in this point start spinning it in unwinding direction.
If the film lead does not come out on its own, use the knife to guide it while unwinding.
Just be careful not to open the case too much, so when you're done, press with your fingers to close it again.
In My case, I had taken some shots (with a film "point an shoot") but I remembered how many, so I took again, the same amount of shots but inside a dark backpack in the darkened room, plus one, And then continued shooting normally.
Result: Somehow I ended shooting 38 exposures out from a 36 exposures film roll, wasting half a frame due to the extra dark shoot (Otherwise the shoots before and after this gap would have been half overlapped).