Have you updated your software to the latest version of Endnote? (Refer to the Endnote software updates page for info.) If you’re up-to-date and the Export to Endnote function is still missing suggest you contact tech support:
For help using EndNote
Monday – Friday, 9 a.m. – 8 p.m. Eastern (GMT -5)
+1-800-336-4474, press 4