How can I update the shipping rates for subscription customers?
Shopify uses the cheapest delivery method rate for all recurring orders. If you have updated this rate, the subscription would need to be cancelled and then re-purchased by your customer in order for a new rate to apply.
As a workaround, you can make a slight change in your customer's subscription which will cause Bold Subscriptions to look for a new shipping rate. For example, you could update the quantity of the product, change the delivery/shipping method, or customer's address, then revert this change so the correct information is properly stored along with the updated rate.
Alternatively, you can create fixed shipping rates in Bold Subscriptions and update your existing subscribers shipping rates at the same time. For more information, please visit this article - https://support.boldcommerce.com/hc/en-us/articles/16114424490900.