If you do not pass your course in IRDAP (and are not awarded) then you will take the reassessment during the following the academic year. Reasons for not passing are because you've deferred or because you've failed the course overall.
For example, if you defer a reassessment that you were due to complete during IRDAP then you will be expected to take that assessment when it normally runs during the following academic year. If it is an exam which normally runs during January then you will take it in January. If it is an exam which normally runs during May/June then you will take it during May/June. Coursework and other assessments will need to be submitted at the same time as students who are having teaching on that course.
Remember that your assessment will take place during the academic year and thus will be ratified only at the end of the academic year, in July. This means that if, for example, you take a January exam whilst you'll get a provisional mark in Winter Term you won't get the final result (and thus can't be awarded) until July. So, even if your programme has an RDAP1 award point in March you can't be awarded because the results for this course will not have been ratified.