401k Withdrawal under Cares Act - Withhold tax now or pay when I file?

Hi, I am filling out paperwork and there is a section for tax withholding. I was planning to claim the income over 3 years. Do I withhold 1/3 of the tax now or can I do no withholding and pay 1/3 when I file my taxes? It seems I should withhold 1/3 of the tax but looking for a definite answer. I don't want any penalties.