"Yin virtue" refers to good deeds done selflessly and without desire for quid pro quo, loyalty, or fame. In Lord Superior Wen Chang's Tract of the Quiet Way, it is mentioned that if your ancestors had accumulated yin virtue, you would enjoy their surplus merits.
Hence, if you receive this lot, you must work hard to repay the kindness of your ancestors by diligently doing good deeds and encouraging others to do good.
Moreover, you must impart the wisdom of the Sages to your children so that they will grow up to be good men and women.
Lastly, to end the repetitive cycle of killing and vengeance that results from eating meat, you must become vegetarian or vegan.