I don't think anyone can really give you a very confidential correct answer.
-It depends how open and deep the scar is, how long is it, what's the cause, and if you don't know it and the scar is not by a clear obvious reason, then diagnosing is so important.
There's so many skin creams, wound creams ect .. . That you can use. But with one wrong choice you can face side effects and cause deeper problems.
So i would suggest you to wait and see if it goes by itself if not and you seen some progress with the scar then check out with a doctor.
Also make sure to check with your cloths and under clothing, maybe the materials that you use causing the problem.