The duplicate option allows you to copy the segment so that it can be refined without adjusting the originally saved segment. To duplicate, click on Audience > Segments and then click the triple-dot menu to the right of the segment that you would like to duplicate.
Click the duplicate option that appears after selecting the triple-dot menu.
The duplicated segment will then open up on your screen. Further refine your data set by selecting different segment criteria.
Click "Save Results" to save your new duplicated segment when you are finished.
Alternatively, you can duplicate a segment by clicking into the segment and click on the arrow menu on the upper-right-hand corner. Select "Duplicate" from the drop-down.