While using Cloud DataWorks's name servers your domain will be pointed to your hosting account, and its active DNS zone will be situated on your Cloud DataWorks hosting server.
In this case you can edit your DNS records directly in Plesk using the DNS Settings.
To change a CNAME record you need to:
Go to Plesk -> DNS Settings -> Adjust the desired CNAME record from the list.
Note that you should set a valid domain/host as destination for the CNAME record as it does not accept IP addresses.