need next.js developer

i have a next.js app that allows users to create dynamic routes, which are currently rendered on my domain. however, i want users to be able to display their routes on a custom domain { user1.mysite.com } instead of my domain { mysite.com }. for this reason, i'm looking for a next.js developer with cloud computing knowledge and who can help me create a wildcard subdomain and ssl. pls see the below attached screenshot and let me know what you understand.

a knowledge of next.js is required because the app is a next.js app.