In RefWorks, open the folder where you are storing the desired references and, if you would only like include some references in your BibTex file, select them using the checkbox next to each reference.
Click on the Share Menu and select Export References from the drop-down menu.
On the window that appears, choose whether you would like to include all or only the selected references in your file, and the type of file format you would like to export them as (in this case it would be BibTex). Click on the Export Button.
A BibTex file should download to your computer.