Problem
You want to delete voicemails in Dialpad but are unsure how to do so.
Solution
Locate the recordings in the Inbox section of Dialpad, and delete them.
Deleting Voicemails on Dialpad
Go to the Dialpad app.
Click Inbox, and then select Recordings.
Find the voicemail you want to delete and hover over it.
Click More
> Delete. 
In the pop-up that opens, confirm your action.