Hello Cathy!
Whether or not a voicemail can be recovered depends completely on how long ago it was deleted. If it was more than 5 days ago, then unfortunately there's no way for us to recover it. If it's less than that though then the number can be easily recovered from the user portal (there's no way for admins to do this for the users).
1) Have the user log into https://login.ringcentral.com/. If it's an admin logging in, click the blue box in the upper right corner of the window and switch it to "My Extension."
2) Click on Messages.
3) Click on Deleted Items.
4) Tick the box next to the message that you want to recover, then click Restore (it's right above the list). The message will be moved back to your inbox and with be placed according to the time and date that it was originally left at.
If you'd like more information on handling messages in the portal, please check out the article below.
https://support.ringcentral.com/article/Checking-incoming-messages-in-my-RingCentral-account.html
~Matt
