There are two basic ways to get the knot out:
1) You may cut the effected portion of your hair or;
2) Soak your hair in hot water for 10 minutes, shampoo the knot and rinse. Afterward apply conditioner and then with a comb, gently work out the knot.
Either way, you should see a professional stylist to either help remove the knot and/or help repair the post knot damage.
Thanks and good luck.