Tried to export a large file in Outlook to archive it, but it exported all files. How do I retrieve the files?

I have Office for Mac 2011. I have been using Office for at least 20 years. 

I am semi retired but occasionally assist my son in law with his work. 

This result in a a large amount of correspondence which is relevant for a while. My Microsoft Identity gets quite large.

I combined a number of files into a file to archive. I selected the file and then selected export with the option to delete old files.

I came back a few hours later to find that all of my Outlook files had been deleted and the .olm contains 2.5gb of data. 

Is it possible to reinstate the information to Outlook?

I ran the Microsoft Database utility yesterday. There has not been much work carried out since the utility run. 

Am I able to select to last file and start with it?