I believe this is something a rep will have to do for you. Unfortunately, the community reps are offline for the weekend. If you have other phone access, you can call 866-347-3292 for customer service. The reps will be back on here on Monday. They're on M-F from approximately 8AM to 5PM EST.
You can also try their chat help, though I don't know if they're online at this time. To do so, click "Contact Us" on the upper right of the page and click Live Chat.
Lastly, it's possible that someone who has HughesNet Voice service may know of a way for you to be able to reset the PIN and they may reply with instructions for doing so, but in the instances I found in searching this community all showed the rep replying and resetting it for them.
Thank you for posting and welcome to the community. I am sorry to hear your voicemail pin is no longer working. You can try dialing *333 if your last four are not going through.
This PDF file http://voice.hughesnet.com/installguide/ has step by step instructions starting from Page 30 (skip to step 5 if you already have an account) or to page 45-46 on how to reset your voicemail password and manage your VoIP service. Do not hesitate to call us at 1-866-347-3292 if you need to be walked through this process over the phone.
We're closing this thread since we never got a reply from you. If you still have concerns, please start a new thread and include a detailed explanation so we can more effectively help you.