Custom NS records for a subdomain

We have a web app hosted on AWS that we want to be a subdomain of our root Squarespace domain. On other platforms, I've been able to achieve this by adding custom NS records in the DNS settings with the subdomain host that point to our Route53 records on AWS. I can access the DNS for our root Squarespace domain, but the dropdown of record types does not include NS records. Has anyone else been able to achieve something similar to what we're trying to do?

Thanks @creedon I'll send this along to the coder and see if this works. I appreciate your quick response!!