I need to find oujt how to get my deceased son's 401K

I am sorry for your loss. It's always best to contact the 401k administrator or HR department for the employer first.  It's possible you are named beneficiary in which case the company should send you claim forms. Or it's possible there is no named beneficiary in which case they will likely give you a form to fill out the family tree. Some plans pay to next of kin and some pay to the estate (probate required if over $150k).  Lastly, it's possible someone else is named beneficiary. If you believe that was not correct and due to fraud, undue influence, mistake, etc... then you would want to hire an estate litigation attorney to fight it. Good luck.