You have to open the coding-big (ini.big for RotWk or edain_data.big for Edain Mod) with FinalBig.
Open the data\ini\weapon.ini and search your Weapon (CreateAHeroEarthShaker_L evel1). Then modify the Damage Value there or the Value of the Macro name (variable), which is in the createaherogamedata.inc for RotWk or in the _gamedata.inc for Edain Mod.