How do I resolve a DNS CNAME conflict from the AWS WordPress Plug-In tool for Cloudfront?

Could you please try the following as per the documentation

https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/CNAMEs.html

Adding an alternate domain name

1. Sign in to the AWS Management Console and open the CloudFront console at https://console.aws.amazon.com/cloudfront/v3/home.
2. Choose the ID for the distribution that you want to update.
3. On the General tab, choose Edit.
4. Update the following values:
Alternate Domain Names (CNAMEs)
Add your alternate domain names. Separate domain names with commas, or type each domain name on a new line.

[...]

Route 53

Create an alias resource record set. With an alias resource record set, you don’t pay for Route 53 queries. In addition, you can create an alias resource record set for the root domain name (example.com), which DNS doesn’t allow for CNAMEs. For more information, see Routing traffic to an Amazon CloudFront web distribution by using your domain name in the Amazon Route 53 Developer Guide.

That is exactly what I have already done. However the final step, going to Route 53 to add the CNAME record is where I have the problem. I get an error message saying "conflicts with other records with the same DNS name in zone" even though there are no other CNAME records visible in my zone.

Based on a DNS query, it looks like you already have an A record for www.diversereads.org - you'll need to remove this to be able to add a CNAME record.

I removed the A record and still got the same error message when attempting to add the CNAME record.