I'm Lizzy, one of the Gurus on the support team at Shopify.
When your account has entered a frozen state you will need to log back in with the account owner email address and update your payment details to be able to pay your bill. You can pay your bill with any of these methods that apply to your location!
This page here talks a bit more about how to unfreeze an account. How long has your store been frozen for?
If you're running into any issues logging in or processing the payment, please feel free to let me know so that I can take a look for you!
What sort of plans do you have for promoting your store's re-opening? Do you have a following on social media or email newsletter subscribers that you can announce it to?