If a process has been created, and it lends itself to being a value stream instead, then the process can be converted. This also works when a value stream needs to be changed into a process.
Quick Steps
Open the item you want to convert
From the diagram content, click on the Actions icon
Select Convert to a Process/ Value Stream
Click Open
Continue editing the converted item like normal
This cannot be done if the process/ value stream is in Approval Declined or Offline status.
To publish the item read more here.