Mailchimp V 123-reg with DNS Settings DMARC entry in DNS

Hi Everyone.
I'm having problems with a DMARC with 123-reg domain settings - Can anyone help me with what the format should be?
the dmarc is from mailchimp and they have told me to create a Cname record with this -

"k1._domainkey.mydomain.co.uk" with the value of "dkim.mcsv.net"

The problems I have/had so far in the past 8 days.
1) 123-reg DNS userface - if you enter the above "k1._domainkey.mydomain.co.uk" it cuts to "k1._domainkey"
2) Got 123-reg to input the full address for me waited 48hrs and the Cname was never listed on any 3rd Party DNS Lookup.
3) Did a full DNS report from MXToolbox and it came up saying that dmarc had Missing or Invalid Record.

after a bit hitting my head on the wall I found this on MailChimp site - which reads -
DKIM requires underscores in the CNAME file. However, in the past, DNS didn’t allow for underscores and some registrars still do not allow them to appear in the CNAME file. If you receive an error to this effect when you attempt to set up your custom DKIM, the issue is on the registrar's side. We recommend that you set up a secondary custom domain specifically for email with a registrar that allows underscores, switch DNS providers, or reach out directly to your current DNS provider about this issue.

I have asked 123-reg to confirm if this would be the problem but still waiting for the tickit to be answered (11Hrs and counting)
So can anyone shed some light on what could be going wrong? - I dont mind holding my hand up and saying its me!! lol
but something isn't working and 123-reg are what can only be said as not very helpful (1st line support that is, can get past that lot)

thanks for any help you can give me.

Regards
Martin.