quickest way to disavow links?

Before the how: are you sure you need to? Google says most sites never should, it already ignores most junk links. It's really for a manual action in Search Console or links you know were paid for. If you do need it, it's a plain text file, one line per site starting with domain: and then the bad domain, uploaded through the disavow tool. Disavowing good links by mistake is how numbers move the wrong way.