Is it possible to merge two outlook.pst files and how do I go about it. Had to revert to a Fall version of Win 10 and I am now missing many emails between today's date and the July pst of that Win 10 version of outlook.pst

Nothing newer than July emails download to Outlook after this revert back to July system image...?...are all emails from July to current Outlook mail lost or can I get them back somehow via current backup of the newer Outlook files in the current Outlook folder(s)