The GP team covers Resetting the Management Reporter data mart at community.dynamics.com/gp/b/dynamicsgp/archive/2019/04/11/resetting-the-management-reporter-data-mart
Resetting the Management Reporter data mart – Microsoft Dynamics GP Community
Reporting & BIMicrosoft & the GP Ecosystem
Archived post from 2019. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.