If someone else has taken your content without asking, here's what you can do:
Reach Out:
Contact the person in charge of the website that copied your content. Tell them you own the content and ask them nicely to remove it.
Use Legal Means:
If they don't answer, you can send them a DMCA notice. This is a legal document that usually makes them take the content down.
Protect Your Content:
Put self-referential canonical tags on your website's content. This helps search engines understand that your content is the original.