If your question is a perfect duplicate, then do what the other answers suggest.
But I have often seen the case where the new would-be asker is under additional constraints. In this case, it's OK to repost - but make sure to
- Link to the original question
- Explain how your situation is different
- Explain why these answers don't work in your specific situation.
The point of duplicate marking is to say "You have the same problem, please use the available solutions". As long as it is obvious that you need a new solution (which is likely to be little relevant or maybe suboptimal for the original asker), it's OK to ask again.