I'll help you out. When you create a new scenario you must open the trigger tab.
Than you create a trigger--> a condition(wen must it happen, by example: object in area,...) You can let it out when you want the trigger to start inmediatly.
Than you create an effect: change object name or change objects attack. When you take change object name you must take select object (and go to object to confirm you have selected the unit). Finally you type the name of the character in the black box.
To change objects attack you must also select the unit and fill in the amount of attack you want it to be increased.
I hope this will do maybe other people can give a better explaination.