Get the error to change on New-AzDisk line -144

[ahsanzakaullah]

When i trying to runn command "$NewManagedDisk = New-AzDisk -ResourceGroupName $resourceGroupName -DiskName $NewDiskName -Disk $diskConfig". I am getting the error.
New-AzDisk: Changing property 'sourceUri' is not allowed for existing disk 'diskName'.
ErrorCode: BadRequest
ErrorMessage: Changing property 'sourceUri' is not allowed for existing disk 'diskName'.
ErrorTarget:
StatusCode: 400
ReasonPhrase: Bad Request
OperationID : b19610a7-e2f3-4408-9ffb-6ff631e53d50