So context i have a game and a encrypted save file. My thoughts were how to find the decryption key in reverse engineering my game .I watched tuts but i think this topic isnt much detailed so i need advice guys.
I voted to close this question because it is, unfortunately, too broad to properly answer.
One has to gain some knowledge and experience in the reverse engineering world before one can tackle some of the real-world scenarios. you may want to start with learning assembly and doing a few crackmes, which are designed to improve one's reverse engineering skills.
Then, you could use this Stack Exchange site to ask specific questions about difficulties and challenges encountered. Alternatively, you can edit this question or post a new one with what you've done so far and what prevents you advancing forward.