Heroes 6 - Discussion

Hello everyone!
I have a silly question.
How do I apply the reinforcement skill (which school is it?) to griffins, and how do I resurrect units in Haven cities?
I can't complete this mission...

Take the second-level reinforcement skill. During battle, select the reinforcement skill and apply it to the griffins.
Build the corresponding special building. At the bottom of the city, a new window will appear after the market and hero hiring window. After the battle, if there were any resurrectable units that were lost, go there and buy back the killed units.