To enable a study for RBM, simply enable the permission for the Data manager or other roles that will be responsible for defining and changing the rules throughout the study.
This is done in Role Security via the Risk-Based Monitoring application.
The only other requirement is that forms in the study, via the form builder, contain at least one FLSV property attribute on a field. It does not need to necessarily be in a field that will be field-monitored. Also, this property is not necessary on a form if there is no anticipated RBM to be done on it.