You call in to VM, pass security using your existing password and then ask the agent to change it.
Or are you asking, "I've forgotten my password and not sure how to change it"? in which case the answer is one of two options..
1: Call into VM as per, and then explain your predicament to the agent. They can ask alternate questions to verify your identity, which are designed to be answerable by the genuine account holder. If no joy, they can post a reminder letter to your home address.
2: Wait on this forum for VM staff to respond, this may take a couple of days. The reminder letter can be posted out.
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