1. Open Outlook

2. Select the "File" Tab at the top left of the screen

3. Select "Open & Export" - "Open Outlook Data File"            

4. A file Explorer tab will open, Locate the PST in question, select it, and hit "OK"   

5. You will then notice the "Outlook Data File" Tab listed under your inboxes, you will be able to open this as if it was its own separate inbox.

NOTE* You can change the name of these Outlook Data Files by right clicking on the inbox and selecting "Data File Properties"