Hi, here's how I've removed this kind of rotor, typical type on vintage Citizens. It's not as simple as the Seiko screw...
There's probably a correct tool for this, but I haven't got one

So I have successfully used the jaws of a measuring caliper, since they are fairly fine, to grip each side of the rotor centre. I found the best way, to minimize risk of slipping and scratching or damaging the movement, was to mount the watch in a case holder, carefully close the jaws onto the centre, then gently turn the case holder (keeping on the desktop so it stays level). I think this keeps the caliper steady since you are not trying to turn it whilst keeping the jaws closed for grip. There may be other and better ways and tools, but this has worked for me. Refitting is of course reverse of removal

Here's pics, not a 6501 but same type of rotor:
Good luck with it - and be careful!,
Sweephand