Assuming that the thread is dead, you have a couple of options, all of which I’ve used successfully. If the crank thread is very knackered, you can’t use it again, so:
a) use a hammer to hit it close to the axle, put weight onto pedal end to try to force it off straight. Have somebody support the frame and rest the BB shell against wood blocks.
b) cut through the crank (saw) at a point that will cut across the hole for the axle, this relieves the tension and lets you tap it off
c) use a gear puller or similar as mentioned above. This is best for nicer/more delicate/more valuable frames.
d) ride it with the end bolt loose as mentioned, but be very careful and stay seated!
Have fun 🙂