Tilda does not provide domain name hosting. It means that you cannot transfer a domain or subdomain to Tilda but you can modify the domain or subdomain records in your domain name registrar account.
Subdomain examples: blog.website.com or www.website.com
Note. It is quite common when only a subdomain points to Tilda while a root domain remains connected elsewhere.
Note. A subdomain can be only assigned to the Tilda website. It means that you cannot assign a subdomain to one of the website pages.
Learn more on connecting a domain: http://help.tilda.ws/customdomain