How do I change phone number in Viber from SIM1 to SIM2, when I only have data on SIM2?

How do I change Viber phone number in a dual-SIM phone from SIM1 to SIM2, when my current Viber account's phone number corresponds to SIM1, but I only have data on SIM2? (e.g. when I have moved to a new network) (The [Viber doc](https://support.viber.com/customer/en/portal/articles/2753274-change-phone-number) does not say how to)