How to clean dried wood stain from paint brush?
You don't.

Once paint dries on a brush, it is uncleanable. Into the trash it goes. 

Even if you soaked it in paint stripper and spent hours working it through the brush, you'd never get the dried paint out of the heel of the brush, nor out of the fine areas on the end of the bristles.   It would never paint right again.  

I don't consider that to be any big deal, since I paint a lot in epoxies and 2-part urethanes.  The brush is a total loss every time, because it would take $10 worth of the exotic solvent to rinse out a brush that is definitely not worth $10.