system
A chat on subreddit /r/wallstreetbets
human
The main thing is you need to be able to say you reasonably didn't know how much money you had in an old dormant account. Best thing to do is come on the Internet and post exactly that you knew the money wasn't yours in front of thousands of witnesses. People never use the Internet to gather evidence,  it's a win win
gpt
The fact he tried multiple amounts, all getting larger is pretty clear evidence of an intent to defraud.   
  
Their only hope is to return the funds and close the account pretending nothing ever happened.  If they lose the money then their only hope is to sign themselves up for some gambling addiction rehab program so when it eventually comes down the pipe they may get leniency.