A CNAME record is stored in your domain’s DNS settings as a pair of values. One value identifies the alias you're creating the record for, which is typically a subdomain. The other value identifies the domain the alias should point to.
With Synup, a CNAME record can redirect the added custom domain links to either scan.synup.com or dashboard.synup.com.
In this way, CNAME records make it easy to run multiple services from one IP address. Each CNAME record associates a service with a domain name, not a physical IP address. The physical IP address is instead identified by your domain's A record. If your IP address changes, you only have to change the A record, not each CNAME record.
Like all DNS records, CNAME records are stored by your domain host and therefore must be changed with the host, not in your Google Admin console.