How do you take wood varnish out of hair?

Use clarifying shampoo asap, it might help lift the stain. If you see no progress, try it a few more times, If you see some removal, wait until the next day and do it again. If the stain is still there the next day you could try colour lifter, but i don't recommend this as i cannot guarantee that it will work, and it may change the colour of the hair you put it on.

Worst case scenario you have to wait for it to come out. It will eventually, but it may take quite a long time.

PLEASE do not use turpentine, it may remove it but it will not make your hair nicer, it is quite possibly the worst thing you could do to your hair.