If you only want to point a subdomain to Uscreen because you want to use your www or root (naked) domains for other purposes you can create a CNAME record to point to Uscreen.
Navigate to the domain you want to set up under My Domains and click the three-dot menu and Manage DNS. Under Records, you'll be either adding a CNAME record for your subdomain if it doesn't exist or editing your existing one.
In the end, you'll want a record like below:
Type - CNAME
Host - whatever you want the subdomain to be i.e. tv or catalog
Points to - lb.uscreen.io
TTL - 1 Hour