You can take the following steps:
Go to the left pane
Click Settings - Phone
Click the Voice Prompts tab
Select the + button, insert the Voice Prompt name, and upload the file
Once the file is uploaded, click Save
Click the General Settings tab
Click Voicemail Prompt and select the uploaded file
Click Save
You can also configure:
Being Recorded Prompt: If you need a record for a quality assurance message
Queue Wait Music: Choose a prompt or music for callers waiting in a queue
Click Settings - Marketing
Click the Campaigns tab
Search for the Campaign(s) that has the phone number you would like to set up the Voicemail, and click Edit
Select Send to Voicemail in the Missed Calls field select your Voicemail in Voicemail Message, and click Save
