Obviously, no-one's ever spoken to you directly about any thing important; however, because you are a foreigner in Thailand finding a lost item, you would be advised not to interfere with it; take a pic of it as you found it, and hand it in. If you opened it and took steps to locate the owner (which is entirely up to you) you run the great risk of being accused with tampering or stealing contents. Why is this so difficult to grasp! Go and annoy someone else.