Hi, first of all, not all reports in BC can be scheduled. This is controlled by the following property of the report.
And this cannot be modified through customization, you can only customize a new report.
More details:
Dynamics 365 Business Central: AllowScheduling and the request page (Schedule… and Multiple Previews) in the Report
Then, which Financial Report to run is specified in the Request Page.
Hope this helps.
Thanks.
ZHU