This comes from an AX focused blog, but the process should be the same for GP when Resetting the Management Reporter 2012 data mart (with CU15+ via Powershell)
Resetting the Management Reporter 2012 data mart (with CU15+ via Powershell) | Dynamics AX in the Field
Microsoft & the GP EcosystemReporting & BIDevelopment & Integration
Archived post from 2016. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.