How do I ensure each Rep can only see the Forecast they own?
In Zoho CRM, you can
set up an organization-wide hierarchy using the Roles module. When it comes to data sharing, users at a higher hierarchy, such as Sales Managers will be able to access the records of someone in a lower hierarchy, like Sales Reps. If you want sales reps to view only the forecasts that they own, set the access to Private. In this case, only the sales rep and his/her manager can view the forecast.