Click Tools.

From the Tools menu, click Export Citation.

From the Export Citation menu, click EndNote, then DOWNLOAD

Save the .txt file to your computer

In Zotero, click File, then Import

At the Import window, keep A file (BibTeX, RIS, Zotero RDF, etc.) selected, then click Next.

Select your downloaded EndNote citation, then click Open

At the Import window, de-select Place imported collections and items into new collection, ensure Copy files to the Zotero storage folder is selected, then click Next.

Your reference should now be imported into Zotero.