This article explains how to export a work plan schedule from OnePlan to use in Microsoft Project.
The OnePlan work plan allows users to export the work plan schedule as an XML file that can be imported into Microsoft Project. This allows you to build a schedule in OnePlan, and then import it into Project Desktop to manage the schedule.
Click on the ellipsis in the Work Plan toolbar > Export > Microsoft Project XML.
See Export the Work Plan List for more information.
Follow the steps detailed in Opening Project XML Files from Microsoft.