How to update customer in Subscription Management?

Summary:

We have subscriptions for multiple customer.

But those customer got merged with another customer and new customer needs to get updated in the subscription.

So we can continue send the invoice to new customer with same subscription.

We tried that and found that Customer field is not updateable.

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Version (include the version you are using, if applicable): 23B

Code Snippet (add any code snippets that support your topic, if applicable):