To change Outlook PST file location after installation, first open Outlook and go to File > Account Settings > Data Files to check where the PST file is stored. Click Open File Location, then close Outlook completely. Next, copy the PST file to your preferred folder or another drive (copying is safer to keep a backup). After that, open Control Panel > Mail > Data Files, remove the old PST entry (this does not delete your data), click Add, and browse to the new location. Set the moved PST file as default and restart Outlook. If you cannot find the PST file, tools like SysInfo PST Converter can help detect it easily.