Tenant burnt wood floor on stairs

Hello,

My previous tenant a frequent smoker left burning cigarette stubs on wooden stairs at least at three different spots and there are very conspicuous dark spots there, I have been putting of remediating this for quite sometime now. What is the best way to address this. I was thinking about putting a white oil paint on top of the dark spots first and then a wood color on top. I appreciate if anyone here can suggest other ideas.

Thanks