I found the answer here
https://support.squarespace.com/hc/en-us/articles/360002101888-Adding-custom-DNS-records-to-your-Squarespace-managed-domain#toc-cname-records
Here are my steps:
In blogger, go to Settings->Publishing->Custom domain and add your new www.xyz.com custom domain that you purchased in Squarespace.
Blogger will respond with a warning that you have to add 2 CNAMES to Squarespace DNS settings. Take a note of those 2 CNAMES.
Open your domain settings in Squarespace Edit DNS.
Delete (red bin) all Squarespace defaults (i took a screenshot before i did this)
Add 2 Custom Records by clicking Add Record. The 2 custom records are the 2 CNAMES in step 2 above.
FInished with Squarespace (i think)
Go back to blogger (step 1 above) and now you can press OK to add your new custom domain.
In blogger I always do Redirect Domain to the new www.xyz.com custom domain, and turn on HTTPS availability and HTTPS redirect (although I am yet to ascertain if this is necessary...
Now give it a few minutes/hours for all the internet records to sort themselves out.
I have checked and yes... now my blogspot redirects to my custom domain 😀
Regards
pesachsteinberg@gmail.com
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DELETE THE SQUARESPACE DEFAULTS:
ADD THE CNAMES TO CUSTOM RECORDS (from blogger custom domain):
FIX THE REST OF YOUR BLOGGER SETTINGS AS FOLLOWS:
