I tend to use two (or even three) large (1ft or more tip to handle end) flat head screw drivers.

Place one on either side, have someone apply even, but not excessive force down on them, say, the same force needed to push down on an old red bike pump hooked to a near inflated bike tire.

Now, making sure to first put the centre bold back on the crank shaft thread, so that the top of the shaft, and the top of the bolt are level (to protect the crank shaft & thread) hit the centre repeatedly with a hammer.

Cheers
Ty

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