A lot of variables here a picture would help a lot,if you can get hold of some OXALIC ACID crystals dissolved in boiling water and then put on the stain(rags tied on the end of a stick )can remove stain. Other than that WOOD BLEACH 1+2 will remove the stain and bleach the wood too so be cautious,apply No1 with a small brush to the stained area and let it dry, rinse the brush out with cold water and then apply No2 to the stained area and watch it rinse off with cold water when you are happy with the colour.
What colour in Nitromors did you use? as it may react with your finish, whats cclstai