Help 18 year old gohan train and unlock mastered beast mode

Help SS2 trunks defeat infinite zamasu. You are a super sayain who can go SS blue evolved and you have friend with you who has been almost killed by zamasu 

He just killed your friend and is about to kill you but you go from super sayain 3 to SS god. He sends a Kamehameha at you and you use instant transmission to go behind him.