How can I change the price of the subscription payment for a single customer?
There isn't a way to change the price of a product for a single subscriber. By default, price changes for subscription products do not affect existing subscribers as they are held to the same terms they agreed to when they first subscribed. Product price changes are only available on the storefront for new subscribers.
As a work around, you can navigate to that customer's subscription in the Subscriptions admin and temporarily swap the product with another, and then swap it back to the original product. This will add the product as a new product with the updated price.
If you need to update the price for all existing subscribers, you can perform a bulk price update in Bold Subscriptions. Read more about the bulk price update tool on our Help Center here: https://support.boldcommerce.com/hc/en-us/articles/25268020454932