First of all, carefully check the payment period on the Japanese national health insurance policy. Even if the policy payment period in some cities is overdue, there is still a time limit for taking it at convenience stores or financial institutions. If you fail, you can also pay at convenience stores and other places.
If you don't have this withdrawal period or both validity periods have expired, the insurance department of the market office will issue you a new late payment policy (that is, to urge you to pay) after a while, and you can pay with this list. Some cities will also charge a late fee of 100 yen ~
In short, don't worry (overdue people often pass by) _