If you are on the Free plan and use up your 5,000 words, you will need to upgrade to a paid plan to get more word quota.

 
For other paid plans, credits reset on the next monthly subscription date. The monthly subscription date is the same as the billing date on your Shopify. We are using Shopify Payment system. So all charges are modified via Shopify. Check this article to know more information.

For the Premium plan, once the 300,000 credit limit is reached and if overcharge is enabled, translations will continue at $9.90 per 30,000 words, up to 3,000,000 words per month. If overcharge is disabled, translations will stop.