If you have some incomplete references in your EndNote, e.g. without a DOI number, or a reference without volume/issue numbers, you may use the Find reference updates to update these references.
Select the references required a update
Go to References > Find Reference Updates
A pop-up box will appear to show the new fields that may require updates. The following image shows that the right column My Reference is the reference in your EndNote library and the left column indicates the fields that can be added to My References.
There are three options in the middle of this pop-up box for updating references.
This example reference contains two missing fields: DOI and Alternate Journal. You can select Update Empty Fields to add both fields to My Reference.
Click Save and Continue
If you don't want to update a suggested field, click Skip.