Currently the Android app does not provide a way to vote to close as duplicate of a question someone already voted to close for.
For example, if user A votes to close question A as a dup of question B, and user B wants to also on the Android app, user B must follow the link, tap the menu, tap share, tap copy to clipboard, tap the back button, tap the menu, tap close, tap duplicate, paste, and tap ok (10 steps). This could be tap menu, tap close, tap duplicate, tap the preset question (4 steps).
Could there be a list of questions previously voted as duplicate?