Use Outlook Repair Toolbox is the best of these Microsoft Outlook PST repair software downloads, letting users quickly and completely restore their lost Outlook messages.
For more: https://www.pstrepairtoolbox.com/
If outlook doesn’t open try rebuilding the ost file. Folder structure might vary a little if you’re on an older OS. Close outlook and in Explorer enable hidden files under View menu. Go to C:\Users\user\AppData\Local\Microsoft\Outlook find the file with extension .ost and add .old at the end. Re-launch outlook. It will take a while to load, since it has to rebuild the local cache file.
Also here’s a link with instructions on how to repair a pst file: