There is such a nice way that I also used to import olm file in to ms outlook by using a Gmail IMAP account. But you can use this approach if you have fewer emails. For this, first you have to configure both Outlook for Mac and Outlook 2010 with that IMAP account. In Outlook for Mac move your mail to a folder in the IMAP account to upload it to the mail server. Now Outlook will automatically download the mail again in the same folder in the IMAP account. It will solve your issue. If your file is too big then this approach is not work for you. In this case, you can use olm to pst converter tools. Many companies offer these tools such as Stellar olm to pst converter, Gladwave olm to pst converter etc.