Find out where the domain is registered with a whois command or goto who.is, then find their copyright/DMCA email and submit a complaint.

For example if it's Namecheap their details to complain are here - https://www.namecheap.com/support/knowledgebase/article.aspx...

GoDaddy here - https://supportcenter.godaddy.com/ipclaims/copyright/infring...

They should take it down pretty quickly if it's a direct copy!