system unstable - how to undervolt 7800x3d?

Hello guys, my system is currently unstable in a way that I get random PC crash once or twice in 2-3 days (mostly while playing games, sometimes idle).

I have a 7800x3d paired with 2 ram sticks 32 GB 6400Mhz CL36 XMP (DCPI) on a asus tuff b650 plus mbo. I just want it to be stable, I just enabled XMP and lowered the speed to 6000. I thought that was enough but it was not ig...

So now i wonder maybe I need to undervolt it? At AUTO with XMP enabled at 6400mhz my CPU vsoc was 1.323 volts and CPU VDDIO / MC Voltage was 1.43.. if i remeber correctly. Then i manualy set soc to 1.2V and VDDIO to 1.35V... again i run into a crash... can someone give me a tip or something am pretty new to this stuff. Should I have additionaly set the offset curve to -10 -20 ?? Is there any step by step guide?