Implement a picker data source that is appropriate to displaying Month/Year selection and converting that selection to a Date answer value.
I recommend implementing a picker that implements the RSDMultipleComponentPickerDataSource protocol. RSDUSMeasurementPickerDataSource has an example implementation for using a picker to select height and weight in US customary units. This would then need to be returned by func dataSource() -> (RSDPickerDataSource?, Formatter) which is defined in an extension of RSDDateRange.