This is not something that can be answered in a forum like this. You need to seek legal advice from a family law attorney as it will depend specifically on the facts of your case and will not necessarily be easy to do. Before you start down the road of attempting to establish paternity, you should also understand what rights and obligations that establishment would mean to you so that you can make an informed decision.
This answer is only for informational purposes, is general in nature and does not constitute legal advice. This Q&A forum does not in any way create an attorney/client relationship. If you have a legal concern that is important to you, I urge you to consult with an attorney as a failure to take prompt and appropriate action on any rights that you may have could be prejudicial to them.