Follow these steps to create a CNAME record. This will help us authenticate your domain.
Verifying your domain
Log in to your Shopify Admin account.
Go to Settings and select Domains.
Click the domain for which you need to add a CNAME record. Click Domain settings and then select Edit DNS settings.
Click Add Custom record and then select the record type as CNAME record.
Specify the Host Name = tec1._domainkey
Specify Points to = tec1.dkim.tinyemail.com
Click Confirm.
Verify your DKIM set up on tinyEmail.
That's it.
Now you know how to create a CNAME record.