Hi,
Alec is right, but often the fork doesn't have a second hole in it making it possible to drift out the remaining part of the pin.
If that's the case with yours, strip away all the removable parts so that the fork can rotate as far as possible. Rarely, a few taps on the fork and/or working it side-to-side might cause the sheered-off portion of the pin to drop out. That's worth a try, but more typically a hole is needed to use a pin punch, as Alec described.
So just drill one as nearly opposite the original (threaded) taper pin hole as you can. It doesn't need to be exactly opposite, just a hole that allows you to get a punch of some sort in there to tap on the end of the pin. Don't make the hole any larger than necessary, to keep from weakening the fork - maybe 1/8" or so. You might need to make a punch out of a bent nail, or something like that, to get behind the fork/shaft as much as possible and still be able to tap on it.
If installing a new fork or an old one that doesn't already have one in it, I'd be very tempted to pre-drill a hole somewhat opposite the taper pin. Sooner or later it will likely be needed. Some planning would be needed, to position the hole so that it's not blocked by the bellhousing when it's finally needed.
There's been a lot of discussion here of ways to reinforce the dreaded taper pin with a secondary fastener and help reduce the likelihood it will sheer off again in the future. I suggest you search the archives.
Hope this helps!
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