Reset Emblems are used to Reset a Hero's Talent Grids.
Using a Reset Emblem recoups 100% of the Emblems spent for the Hero.
If you do not have Reset Emblem, you can still Reset your Talent Grid by using Gems, however, you will receive only 95% of the Emblems back that you have spent on the Hero.
Reset Emblems can be received as loot from Alliance War Chests and Raid Tournaments.
Please note - it is only possible to choose one direct path to the final Talent. If you have made a mistake, you can always reset your Talent Grid with a Reset Emblem.