Update bibliography option not working in MS Word

I have inserted citation using EndNote in MS Word (Mac OS) and when I try to open the same file in Windows OS, the citations that are already inserted are not treated as an EndNote citation. Can anyone help me with this problem? 

I would try the following:

First, make a back-up of your document by saving it with a new name. Then unformat using the instructions for your versions of Word and EndNote:

Word 2013/2016 Win with EndNote X7: Go to the EndNote tab and choose the “Convert Citations and Bibliography > Convert to Unformatted Citations” command.

Word 2016 Mac with EndNote X7 and later: Go to the EndNote tab and choose the “Tools > Convert to Unformatted Citations” command.

Word 2010 with EndNote X4 and later or Word 2007 with Endnote X1 and later: Go to the EndNote tab and choose the “Convert Citations and Bibliography > Convert to Unformatted Citations” command.

Word 2007 with Endnote X and earlier: Go to the Add-Ins tab and choose the “EndNote > Unformat Citations” command.

Word 2008/2011 with EndNote X5 and later: Go to the Tools Menu and select “EndNote > Convert to Unformatted Citations” command.

Word X/2000/2002 (XP)/2003/2004/2008/2011: Go to the Tools Menu and select “EndNote > Unformat Citations” command.

This should revert all the citations into the temporary citation format and remove the reference list from the end of the document. Then, format the document.

Any version of Word and EndNote: Click on Go to EndNote in Word. Go up to Tools then Cite While You Write in EndNote and click on Format Bibliography on the new window click OK.

EndNote will pick up the reference information from your open library or libraries, and the changes will be picked up.

You can find this information online as well.

https://support.clarivate.com/Endnote/s/article/EndNote-Updating-a-Word-document-to-match-changes-from-your-EndNote-library?language=en_US

If the document does not format then please contact Technical Support:

1-800-336-4474 option 4 then 1

or
https://endnote.com/contact/