I'm unsure if the details of that process are public but presumably it is possible through coordination with the bank, the treasury department, or both. What I could find publicly was that CZ's personal fine of $70m is payable either by ETF, cashier's check or money order.

EDIT: This rabbit hole also led me to find out that this year, British American Tobacco has a $500m fine for violating some Weapons of Mass Destruction regulation. It sounds horrifying but they basically sold equipment to make cigarettes to the DPRK and tried to hide it. It's confronting seeing proof how blatantly corporations act. There was actual people who decided to do this.