Disclaimer: We haven’t used OmniFocus so we don’t really know, but recently a user shared the following steps, which should help you import data from OmniFocus (or other similar Task Managers).
Article ID: 721
Created On: Sat, Feb 6, 2016 at 4:02 PM
Last Updated On: Sat, Feb 6, 2016 at 4:02 PM
Online URL: https://www.2doapp.com/kb/article/how-do-i-import-data-from-omnifocus.html