While the change suggested by Steve, will fix the problem with this style, assuming you want the full title or abbreviation as it is in the Journal field, it will not fix it for the next style or adjust for full title or abbreviated journal - which is the power of Endnote and the Journal Terms list and settings. If you want a short cut, you need to edit the Journal Terms list, because that is where it is pulling the “sentence case” version, if you don’t want to change the output style.
The correct fix is outlined in the link he also provided. Fix your library’s Journal Terms list and turn off the preferences which update the Journal Terms list based on the Journal and Alternative Journal fields downloaded from databases.