Download and install SysInfo Outlook PST Unlocker as an administrator.

Then, click on the Select Files Button to add the Locked PST File.

Choose the PST file that you want to unlock.

Click on the Unlock PST Button and your PST will be unlocked.

Now, you can click on the Set Password Button to add a new password to the PST File.

Enter the Password confirm, and click on OK.

You will receive a confirmation when your PST file is locked again with your desired password.