"Overpayment" is another way of saying refund. The question is asking if you want your refund to go toward paying your taxes for tax year 2020.
An overpayment is your refund. You can have them keep all or part of your refund as an estimated payment towards next year's tax return. But most people want to get their refund now. So to get your refund now do not say to apply it to next year.