|Couple steps to get back your password below...|
1. Microsoft Outlook has no retrieval option for .pst folder passwords, so keep your password in a safe place, and make it something that you will easily remember but that would be hard to guess.
2. Enter your password in the pop-up box labeled "Personal Folders Password."
3. Keep trying different passwords, as you will not be able to reset your .pst password or access the files without the proper password.
In case it doesn't work for your case, then you may read useful resources with more variants of recovering