How do you disavow links in ahrefs?

One caveat on the export: check the format before uploading. Google wants one entry per line, and a whole domain goes on a line starting with domain: followed by the domain. A new upload replaces the old file completely, so always add to your previous list rather than starting over, or you'll quietly undo everything you disavowed before.

Ahrefs only builds the file, it doesn't send anything to Google. In Site Explorer's backlinks or referring domains report you can mark links or whole domains for disavow, then export the list as a txt. That file then goes into Google's own disavow tool for the Search Console property. Before you do any of it though, Google's line is that most sites never need to disavow, it mostly ignores spammy links on its own. It's really meant for when you've had a manual action or you know links were bought. Disavowing the wrong domains can do more harm than leaving them.